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\input texinfo   @c -*-texinfo-*-
@copying
Copyright @copyright{} 2014, 2015 Mattias Andrée (@email{maandree@@member.fsf.org})

@quotation
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
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``GNU Free Documentation License''.
@end quotation
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@c %**start of header
@setfilename mds.info
@settitle mds -- The avant-garde micro-display server
@documentencoding UTF-8
@documentlanguage en_GB
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@dircategory Graphics environment
@direntry
* mds: (mds).                        The avant-garde micro-display server.
@end direntry

@documentdescription
User and developer manual for mds, the avant-garde
micro-display server, and servers, protocols,
libraries and concepts.
@end documentdescription
@c %**end of header



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@defindex op
@defindex sg
@defindex ub
@defcodeindex pr



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@ifnottex
@node Top
@top mds -- The avant-garde micro-display server
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@titlepage
@title mds
@subtitle The avant-garde micro-display server
@ifset LOGO
@vskip 0pt plus 1filll
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@item @tab @center @image{../logo,250px}
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@vskip 0pt plus 2filll
@end ifset
@author by Mattias Andrée (maandree)

@page
@center `To me, writing a monolithic system in 1991 is a truly poor idea.'
@c  Well, here we are 23 years later, and we are still
@c  doing it, but where it is even easier not to.
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@c If you prefer a dead tree edition, you can order one from
@c ...
@c @*
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@shortcontents
@contents



@menu
* Overview::                        Brief overview of @command{mds}.
* Architecture::                    Architectural overview of @command{mds}.
* Application Design::              Guildlines for your applications.
* Protocol::                        The @command{mds} procotol.
* Utilities::                       About @command{mds} utilities.
* Servers::                         About @command{mds} servers.
* Protocols::                       @command{mds} procotols.
* libmdsserver::                    Overview of @command{libmdsserver}.
* mds-base.o::                      Overview of @file{mds-base.o}.
* Keyboard Codes::                  Scancodes and keycodes.
* Keyboard Layouts::                Writing and compiling keyboard layouts.
* Default Keyboard Layouts::        The keyboard layouts installed with @command{mds}.
* Accessibility::                   Dealing with disabilities.
* Specifications::                  Specifications.
* New Concepts::                    Discussion of new display server concepts.
* Discussion::                      Discussion on display server-architecture.

* GNU General Public License::      Copying and sharing @command{mds}.
* GNU Free Documentation License::  Copying and sharing this manual.

* Program index::                   Index of servers, clients and utilities.
* Variable index::                  Index of environment variables.
* Option index::                    Index of command line options.
* Concept index::                   Index of concepts.
* Signal index::                    Index of signals.
* Function index::                  Index of functions.
* Data type index::                 Index of data types.
* Unicode block index::             Index of Unicode block.
* Protocol index::                  Index of @command{mds} protocols.
@end menu
@c TODO @detailmenu (`C-c C-u m`)



@node Overview
@chapter Overview

@command{mds}@footnote{mds stands for micro-display
server.} is a display server protocol and an
implementation of said protocol. What makes
@command{mds} stand out is its core design choice:
it is desigend just like a microkernel. Rather than
one, possibly modular, process --- a monolithic
process --- @code{mds} is comprised of many small
servers, each exchangable and responsible for one
thing.

@cpindex Goals of @command{mds}
@command{mds}'s goal is neither security, performance
nor a perfect graphical experience. @command{mds} is
all about flexibility and freedom 0@footnote{The
freedom to run the program as you wish, for any
purpose.}.

The reason for having a display server architectured
as a microkernel is so that components can be added,
removed, updated and replaced online. Additionally,
the message passing between the servers makes it easy
to design a system that lets you make clients that
can listen on messages between the servers and
perhaps modify them. This enables you to do so much
more with your display server. Moreover, if a single
part of the system crashes it does not bring down the
whole system, and the crashed server can be respawned
with minor side effects. @command{mds} is
architectured in three layers: a microkernel, a
master server and a collection of servers. And
clients are actually located on the same layer as the
servers, because there is no actual difference, the
only thing that separates a server from a client is
for what purpose you run it. @command{mds}'s kernel
is a minimal program that do initialisation of the
display, such as giving it an index and create
runtime files and directories for servers and other
programs to use. Then the kernel creates a domain
socket for the master server and spawns the master
server and respawns it if it crashes. Because of
this, if the master server crashes it will not lose
its socket when it is respawned. The master server
then, on its initial spawn, starts the all servers
and other programs that the user have choosen and
then starts accepting connections to it and
coordinates messages between servers and clients.
Further, separating all components into separate
processes enables us to only give the servers the
privileges they actually need, rather than having
one program with root privileges that takes care of
everything even things that do not do require any
privileges.

All @command{mds}'s servers, that is all running
parts of @command{mds} except the kernel, are
designed so that they can re-execute themself so that
they can be updated online without any side effects.
Servers serialises their state, saves it to RAM (in a
directory created by the kernel), re-execute themself
and loads their serialised state. The kernel cannot
do this because when it has spawned the master server
it has no reason to re-execute, its only mission is
to respawn the master server it if would happen to
crash. It would technically be possible to enable the
kernel to re-execute but it is not worth it as there
is no reason to re-execute, and doing so puts the
display server at risk of crashing.



@node Architecture
@chapter Architecture

@menu
* Layers::                          The layers of the display server.
* Interprocess Communication::      How servers and clients communicate.
@end menu



@node Layers
@section Layers

@cpindex Layers, architecture
@cpindex Architectural layers
@cpindex Kernel
@cpindex Display server kernel
@pgindex @command{mds}
@cpindex Master server
@pgindex @command{mds-server}
The @command{mds} display server in architectured in
three layers. The first layer is called the kernel.
The kernel is responsible for acquiring a display
server index@footnote{As with any display server, the
system can have multiple instances of @command{mds}
running at the same time.}, set up environment
variables to indicate which display server and
display server instance is being used, create a
domain socket for the display server and start the
master server and restart it if it crashes, and then
clean up the system when the display server closes.
The kernel only responsible for creating the domain
socket for communication with the display server, it
is not responsible for using it, that mission falls
to the master server.

@cpindex Master server
@cpindex Message passing, coordination
@cpindex Communication, coordination
@cpindex Interprocess communication, coordination
@pgindex @command{mds-server}
The second layer is the master server. The master
server has two responsibilities: coordinating
message passing between other servers and clients
@footnote{In @command{mds} there is no functional
distinction between servers and clients, the
distinction is purely semantic.} and starting other
servers.

@cpindex Starting of servers
@cpindex Servers, starting
@pgindex @file{mdsinitrc}
The third layer is the other servers and clients.
protocolwise there is no specification on how they
are started. But in the reference implementation of
the master server, this is done by starting a shell
script with the pathname
@file{$@{XDG_CONFIG_HOME@}/mdsinitrc} and the user
is responsible for providing the logic in that shell
script.@footnote{Moonstruck users are allowed to
implement this in C or any other language of their
choosing.}
@c Which is better: cray-cray users, lunatic users,
@c moonstruck users, insane users, ballers, madmen,
@c loony tunes, systemd-lovers?
These servers implements the actual functionality
of the display server.



@node Interprocess Communication
@section Interprocess Communication

@cpindex Message passing, mechanism
@cpindex Communication, mechanism
@cpindex Interprocess communication, mechanism
@cpindex Master server
@pgindex @command{mds-server}
Intrinsic to @command{mds} is a powerful interprocess
communication mechanism. Servers and clients connect
to the display server by connecting to a domain
socket served by the master server. A server or
client that has connected to the display server can
do three things:

@itemize
@item
Request assignment of a unique ID@.
@item
Multicast a message.
@item
Join or leave a multicast group.
@end itemize

@cpindex Multicast groups
@cpindex Client ID assignment
@cpindex ID assignment
@cpindex Assignment of ID
@cpindex Disconnection
@cpindex Master server
@pgindex @command{mds-server}
Upon assignment of an ID the master server will
automatically place the client in a multicast group
for that specific client. This automatically
multicast group assignment is done by the master
server simply so you as a debugger do not forget to
do so. When a client is disconnected it will send
out a message to a specific multicast group that the
client, refered to by it's ID, have closed.

@cpindex Message passing, message structure
@cpindex Communication, message structure
@cpindex Interprocess communication, message structure
@cpindex Message structure, message passing
@cpindex Master server
@pgindex @command{mds-server}
A message in the @command{mds} protocol is comprised
of two parts: headers and a payload. When a client
joins a multicast group it is actually saying that
it is interested in receiving broadcasts containing
a specific header or a specific header--value pair,
or that it is interesting in all messages
@footnote{This could be used for logging, possibly
spying and networking.}. Thus a message is
automatically multicasted to groups indicated by its
headers.

@cpindex Interceptions, message passing
@cpindex Message passing, message modification
@cpindex Communication, message modification
@cpindex Interprocess communication, message modification
@cpindex Message modification, message passing
@cpindex Master server
@pgindex @command{mds-server}
@cpindex Multicast groups
The multicast groups and receiving of message is
called interceptions. The interesting property of
interceptions is that they may be modifying. When a
server registers for message interception it can say
that it wants to be able to modify messages. If this
is done and the server receives a message for which
it has said it want to be able to modify it, the
master server will wait for that server to respond
before it send the message to the next server in the
interception list. The server can choose to do three
things with a message that it has opted in for
modification of: leave the message as-is, modify the
message, or consume the message. A message
consumption is done by modify the message to make it
empty. A consumed message will not be send to any
further clients or servers in the interception list.

@cpindex Interception priority, message passing
@cpindex Priority, interception, message passing
@cpindex Message consumption, message passing
@cpindex Consumption, interception, message passing
To make this mechanism sensible, a server or client
can set a priority when it registers for interception
(does not need to be modifying.) When a message is
broadcasted it will be received by all servers in the
interception except the original sender, unless it
gets consumes. The order in which the master server
sends the message to the recipients is determined by
priority the servers registed with. The message first
sent to the recipients with highest priority and last
to the recipients with lowest priority, and ordered
by the priority between those priorities. Of two or
more servers have the same priority the order in
which they will receive the message, of those
recipients, is arbitrary.

@pgindex @command{mds-vt}
@cpindex Virtual terminal, switching
@cpindex Switching virtual terminal
@cpindex Dual-connection, message passing
@cpindex Message passing, dual-connection
@cpindex Communication, dual-connection
@cpindex Interprocess communication, dual-connection
@cpindex Reflexive connection, message passing
An interesting property of this mechanism is
demonstrated in the @command{mds-vt} server. Unlike
most servers @command{mds-vt} maintains two
concurrent connections to the display. Once
@command{mds-vt} receives a signal from the OS
kernel requesting to switch virtual terminal,
@command{mds-vt} will from one of its connections
send out a message and wait for it to be received
in its other connection and the let the OS kernel
switch virtual terminal. The secondary connection to
the display has registered interception with lower
priority of the message than the primary connection
broadcasts. This message will be received by other
servers that will let the message continue to the
next server in the interception list once that server
is ready for the OS kernel to switch virtual
terminal. All of these servers have registered
modifying interception of the message but none of
them will actually modify or consume the message; it
is only used a mechanism for letting @command{mds-vt}
know when all servers are ready for the switch
without having to know how many they are and wait
for a reply from all of them.



@node Application Design
@chapter Application Design

@cpindex Application design
@cpindex Client design
@cpindex Guildlines, applications
@cpindex Toolkit guildlines
When creating graphical @command{mds} applications,
there are some guildlines you should follow.

@itemize @bullet
@item
@cpindex Client-side decoration
@cpindex Server-side decoration
@cpindex Decoration, guildlines
@b{Do not create client-side decoration}. Some users
do not want decorations or wants minimal decorations.
Windows should look similar, server-side decoration
helps ensure this. Your client-side decorations may
not meet the requirements the users have. For
example, your client-side decoration may only support
minimise, maximise and close, whilst the user may
also want, as provided by her decoration server,
stick, shade and always on top. And it should be
sufficient to configure your decorations once rather
once for every toolkit. Additionally, because of
oversight from developers, client-side decoration
tends to work poorly with tiling window managers.

@item
@cpindex Memorisation of size and position
@cpindex Position, memorisation
@cpindex Size, memorisation
@pgindex @command{mds-posmem}
@b{Do not remember size and position}. Some users
do not want their programs to remember their size
and position. There is also a risk that your
mechanism for implementing this does not account for
the possibility that outputs may have been removed,
resized or relocated. @command{mds-posmem} can be
used if the user wants programs to start where they
were closed the last time they were closed.
@end itemize



@node Protocol
@chapter Protocol

@menu
* Environment Variables::           Identifying the active display server.
* Signals::                         Signalling individual servers.
* Filesystem::                      The display server's footprint on the filesystem.
* Message Passing::                 Sending messages between servers and clients.
* Interception::                    Implementing protocols and writing unanticipated clients.
* Portability::                     Restrictions for portability on protocols.
@end menu



@node Environment Variables
@section Environment Variables

@cpindex Environment variables
@vrindex @env{DISPLAY}
@vrindex @env{MDS_DISPLAY}
@cpindex Display server identification
@cpindex Identification, display server
A crucial task of any display server is letting child
processes know which display server they should
connect to. @command{X.org} does this by setting the
environment variable @env{DISPLAY} to
@code{<host>:<display index>}, where @code{<host>}
is empty if the display is one the local machine.
In this tradition @command{mds} does the same thing
with the environment variable @env{MDS_DISPLAY}@.

@cpindex Environment variables
@vrindex @env{MDS_PGROUP}
@cpindex Display server process group
@cpindex Process group, display server
@command{mds} also creates a new process group and
export the new process group ID to the environment
variable @command{MDS_PGROUP}@. This process group
can be used to send signals to all @command{mds}
servers collectively.



@node Signals
@section Signals

@cpindex Signals
@cpindex Re-executing servers
@cpindex Updating, online
@cpindex Online updating
@cpindex Version update
@sgindex @code{SIGUSR1}
@sgindex @code{SIGUPDATE}
@command{mds} servers can re-execute into an updated
version of their binary. This can be used to update
display server online after a new version has been
installed. To do this send the signal @code{SIGUSR1}
to the server you want update. If a server does not
support online updating it will ignore this signal.
If the operating system defines a signal named
@code{SIGUPDATE}, this signal is used instead of
@code{SIGUSR1}.

@cpindex Signals
@cpindex Memory release, automatic
@cpindex Memory release, forced
@cpindex Automated memory release
@cpindex Forcing memory release
@cpindex Releasing memory
@sgindex @code{SIGDANGER}
@sgindex @code{SIGRTMIN + 1}
If you need servers to free up allocated memory that
they do not use, send the signal @code{SIGDANGER}, or
if not defined @code{SIGRTMIN + 1}. Unimportant
servers may choose to die on @code{SIGDANGER}@.

@sgindex @code{SIGINFO}
@sgindex @code{SIGRTMIN + 2}
@cpindex State dump
@cpindex Statistics dump
Server may also choose to support the signal
@code{SIGINFO}, or if not defined
@code{SIGRTMIN + 2}. It is not expected that server
do support this signal, but thay must not die when
received. @code{SIGINFO} is send by a user to the
server, if she wants the server to dump information
about the server's state or statistics to the TTY@.

@sgindex @code{SIGRTMIN}
@cpindex No-operation signal
All servers configured to be interrupted when the
signal @code{SIGRTMIN} is received. No further action
is taked. This may be used by the user to test that
the program supports being interrupted. It can also
be used by the server to interrupt itself from another
thread.

@pgindex @command{valgrind}
@sgindex @code{SIGRTMAX}
@command{valgrind} uses @code{SIGRTMAX} for its own
internal stuff. Therefore servers must not use
@code{SIGRTMAX} as it is hence unavailable when
running under @command{valgrind}.



@node Filesystem
@section Filesystem

@cpindex Interprocess communication, filesystem
@cpindex Filesystem
@cpindex Kernel
@cpindex Display server kernel
@pgindex @command{mds}
The @command{mds} kernel creates two directories for
the @command{mds} servers to use: one for runtime
data and one for temporary data. These directories
are named by @code{MDS_RUNTIME_ROOT_DIRECTORY} and
@code{MDS_STORAGE_ROOT_DIRECTORY}, respectively,
by the header file @file{<libmdsserver/config.h>}.
If the systems runtime data directory is @file{/run}
and transient temporary data directory is @file{/tmp},
and the package name of @command{mds} is
@command{mds}, these directories will be
@file{/run/mds} and
@file{/tmp/.@{system-directory@}.mds}, respectively.
In @file{/tmp/.@{system-directory@}.mds} the kernel
will create a directory for the display server
instance named @file{.data} prefixed by the display
server index. For example if the display server index
is zero, temporary data may be stored in
@file{/tmp/.@{system-directory@}.mds/0.data}

@cpindex Re-executing servers
@cpindex Updating, online
@cpindex Online updating
@cpindex Version update
As defined by @code{SHM_PATH_PATTERN} in
@file{<libmdsserver/config.h>}, when a server
re-executes itself it will marshal its state to
the POSIX shared memory unit named
@file{/.proc-pid-%ji}, where @file{%ji}
@footnote{@code{%ji} is the pattern in @code{*printf}
functions for the data type @code{intmax_t}.} is
replaced with the process ID of the server. This
file will be bound to the pathname
@file{/dev/shm/.proc-pid-%ji} if POSIX shared memory
is stored in @file{/dev/shm} by the operating system.

In @code{MDS_RUNTIME_ROOT_DIRECTORY} the kernel will
create two files. @file{.pid} and @file{.socket},
both prefixed with the display server index
@footnote{@file{0.pid} and @file{0.socket} if the
display server index is 0.}. The @file{.pid} file
contains the process ID of the display server and is
used by the kernel to figure out whether an display
server index is still in use or just not properly
cleaned up. Of course it can be used by any program
to find the process ID of the kernel process of a
display server instance. The @file{.socket} is the
domain socket used for communication with the display
server and its servers and clients.



@node Message Passing
@section Message Passing

@cpindex Message passing, display
@cpindex Communication, display
@cpindex Interprocess communication, display
@cpindex Kernel
@cpindex Display server kernel
@pgindex @command{mds}
Message passing over domain sockets is the
underlaying technique for communicating with the
display server. To communicate with the display
server in the local machine a process must connect
to the domain socket created by the display server
kernel as named in @ref{Filesystem}.

@cpindex Connecting to the display
@cpindex Client ID assignment
@cpindex ID assignment
@cpindex Assignment of ID
Clients should request a unique ID when it
connects to the display server.@footnote{There
is seldom a reason for servers to do this.}
To do this the client sends

@example
@group
Command: assign-id\n
Message ID: 0\n
\n
@end group
@end example

@cpindex Message ID
@cpindex Message corruption
@cpindex Corrupt messages
where @code{\n} is an LF-line break. The value on the
@code{Message ID}-line does not need to be 0, but
servers and clients often start with 0 and count
upwards. The value is however bound to an unsigned
32-bit integer. All message must contain this
@code{Message ID}-header, otherwise the message is
considered corrupt and is ignored.

@cpindex Message structure
@cpindex Message passing, message structure
@cpindex Communication, message structure
@cpindex Interprocess communication, message structure
The empty line signifies the end of the header list,
and in this case the end of the message. But a
message may contain payload beneath this empty line.
To include a payload, add the header @code{Length}
that says how many bytes the payload is comprised.

A header must contain a header name and header value
without any trailing or leading spaces, and `: '
(colon, one regular blank space) exactly delimits
the name and the value.

@cpindex Master server
@pgindex @command{mds-server}
@cpindex Client ID assignment
@cpindex ID assignment
@cpindex Assignment of ID
When the master server receives this
@code{Command: assign-id}-message it will assign the
client a unique ID and send it to the client.
@footnote{The master server is the only server than
can address the client uniquely before it has an ID,
so this part can only be implement in the master
server.} If the client already has an ID, it will
send back that ID to the client. This response
consists of two headers @code{ID assignment} and
@code{In response to}, containing the client's
new (or possibly already assigned) ID and the value
that was in the @code{Message ID}-header,
respectively. For example:

@example
@group
ID assignment: 0:1\n
In response to: 0\n
\n
@end group
@end example

@cpindex Message ID
Notice that the master server never includes
@code{Message ID} in message originating from it.

As seen in this example, the client ID consists of
two integers delimited by a colon (`:'). Both of
these integers are unsigned 32-bit integers. This is
done this way because unsigned 64-bit integers are
forbidden because it is not supported natively be
some programming languages.

Before a client has gotten a unique client ID
assigned to it, it will be `0:0'.

@cpindex Disconnection
If a client gets disconnected from the master server,
the master server will sends out a signal header
message. This header will be @code{Client closed}
and contain ID of the client that closed. For example:

@example
@group
Client closed: 0:1\n
\n
@end group
@end example

Be aware that if a server or client closes and does
not have a unique client ID, this message will be:

@example
@group
Client closed: 0:0\n
\n
@end group
@end example

@cpindex Addressing message
@cpindex Message passing, addressing
@cpindex Communication, addressing
@cpindex Interprocess communication, addressing
Once a client has an unique client ID assigned to it,
it should always include the header @code{Client ID}
in its messages. The value of @code{Client ID} should
be the client's ID@. If a server wants to address
this client, it should include the header @code{To}
with the value set to the recipient's client ID@.
Be aware that such message may not be sent to that
recipient uniquely, any server or client is free to
sign up for receive of such message, any messages
or message contain any other header or header--value
pair that may also be included in the header.



@node Interception
@section Interception

@cpindex Interceptions, message passing
@cpindex Message passing, message modification
@cpindex Communication, message modification
@cpindex Interprocess communication, message modification
@cpindex Message modification, message passing
@cpindex Interceptions, eavesdropping
@cpindex Message passing, eavesdropping
@cpindex Communication, eavesdropping
@cpindex Interprocess communication, eavesdropping
@cpindex Eavesdropping, message passing
As discussed in @ref{Interprocess Communication},
interception in the primary feature of
@command{mds}'s message passing system. Not only does
it enable servers to select which message it wants to
receive in order to provide it's service. It also
enables clients to do anything, things that was never
anticipated. As an example of its power,
@command{mds} does not provide any protocol for
taking screenshots or recording a session. Instead,
a screenshot application signs up for messages passed
between the compositor and presentation servers, and
simply requests that the compositor resends the
screen, a feature intended for the presentation
servers. A screen recoding application would do the
same and just hang on and record all message passed
between the servers.

If you want your server or client to receive all
messages passed around in the display server, simply
sign up for all messages:

@example
@group
Command: intercept\n
Message ID: 0\n
\n
@end group
@end example

But if you only want messages contain the header
@code{Command}, include that header in the payload
of the message:

@example
Command: intercept\n
Message ID: 0\n
Length: 8\n
\n
Command\n
@end example

It is allowed to include multiple headers. You can
also be more strict, and require a specific value
for a header, for example:

@example
Command: intercept\n
Message ID: 0\n
Length: 16\n
\n
Command: get-vt\n
@end example

You may mix these two types of requirements freely.
Your client will receive any message that satisfies
at least one of the requirements, these requirements
may be split into multiple message or coalesced into
one message; but you cannot request to include
receive a message if multiple requirements are
satisfied.

Alternatively you can choose to stop receiving
message that satisfies requirements. For example:

@example
Command: intercept\n
Stop: yes\n
Message ID: 1\n
Length: 16\n
\n
Command: get-vt\n
@end example

Or stop receiving all messages:

@example
Command: intercept\n
Stop: yes\n
Message ID: 1\n
\n
@end example

Note that this will stop you from receiving messages
contain the @code{To}-header addressed to you until
you request to receiving such messages again.

When you sign up for message you may request to be
able to modify them before that are send to the next
client in the list of client that should receive
them. To do this include the header--value pair
@code{Modifying: yes}:

@example
Command: intercept\n
Modifying: yes\n
Message ID: 0\n
Length: 30\n
\n
Command: keyboard-enumeration\n
@end example

It is up to the client to keep track of which message
that it may modify. When you receive a message that
you can modify you must respond when you are done
with the message.

For example, if you have signed up for
@code{Command: keyboard-enumeration} with the ability
to modify such messages and the message

@example
Command: keyboard-enumeration\n
To: 0:1\n
In response to: 2\n
Message ID: 1\n
Length: 7\n
\n
kernel\n
@end example

is send from a server, you may receive it as

@example
Command: keyboard-enumeration\n
To: 0:1\n
In response to: 2\n
Message ID: 1\n
Length: 7\n
Modify ID: 4\n
\n
kernel\n
@end example

Be aware that the @code{Modify ID} may be included
even if you have not signed up to be able to modify
the message, it is enough that one client before you
has or it was originally included @footnote{You may
however not include this header when you send out an
orginal message.}.

If you receive the message as such and want to add
the line @code{on-screen-keyboard-20376} to the
payload should send out: @footnote{The first line
containing starting with @code{Message ID} is an
example, it should be whatever is appropriate for
your client.}

@example
Modify ID: 4\n
Message ID: 2\n
Modify: yes\n
Length: 127\n
\n
Command: keyboard-enumeration\n
To: 0:1\n
In response to: 2\n
Message ID: 1\n
Length: 32\n
Modify ID: 4\n
\n
kernel\n
on-screen-keyboard-20376\n
@end example

If you however decide not to modify the message send
out

@example
Modify ID: 4\n
Message ID: 2\n
Modify: no\n
\n
@end example

@cpindex Message consumption, message passing
@cpindex Consumption, interception, message passing
There is also a third option: to consume to the
message. This stops any further clients from
receiving the message. This is done by modifying the
message into an empty message:

@example
Modify ID: 4\n
Message ID: 2\n
Modify: yes\n
\n
@end example

You may choose to include the header--value pair
@code{Length: 0}, it is however redundant and
discouraged.

@cpindex Interception priority, message passing
@cpindex Priority, interception, message passing
This mechanism of being able to modify message does
not make much sense unless you can control in the
order the clients receive messages. This is done with
what is called priority. The higher priority you
have, the earlier you will receive the message. The
default priority is zero, and the priority is bound
to a signed 64-bit integer. If you want to be able to
list yourself in @code{Command: keyboard-enumeration}
message, you should sign up with a positive priority
since the final recipient or requested the
enumeration will receive it with priority zero.
Therefore you should sign up for such message with a
message like: @footnote{4611686018427387904 is
halfway to the maximium value.}

@example
Command: intercept\n
Modifying: yes\n
Priority: 4611686018427387904\n
Message ID: 0\n
Length: 30\n
\n
Command: keyboard-enumeration\n
@end example



@node Portability
@section Portability

@cpindex Portability
For optimal portability, there are some restrictions
on protocols.

@itemize @bullet{}
@item
@cpindex Integers, minimum value restriction
@cpindex Minimum value restriction on integers
@cpindex Restrictions on minimum value for integers
Because C allows unsigned integers to be encoded as
either sign and magnitude, one's complement or two's
complement@footnote{GCC only allows two's complement},
the minimum value of any signed value with a fixed
bit-size is the negative of its maximum value, that
is, the minimum value @code{int16_t} is to be assumed
to be @code{-INT16_MAX} (@math{-32767}) rather than
@code{INT16_MIN} (@math{-32768} with two's
complement.)

@item
Integers that are not especially encoded must not be
larger than 64-bits if they use fixed bit-size. If,
for example, @code{size_t} is 128-bits on your
platform but you are using a language that only have
native integers up to 64-bits you must use arbitrary
size integers or otherwise make sure that the value
can be properly stored and used.

@item
@tpindex @code{uint64_t}
@cpindex Integers, unsigned, restriction
@cpindex Unsigned integer, restriction
@cpindex Restrictions on unsigned integers
Integer 64-bits that are not especially encoded must
not be unsigned if the bit-size is fixed. This is
 because some programming languages primitive
integers are limited to 64-bits and are signed; a
large enough unsigned 64-bit integer would overflow.

@item
@cpindex Endianness, portability
Native endianness when a endianness is choosen. Do
not assume big endianness, but the same endianness
that appear on the same machine when using C@.

@item
@cpindex UTF-8, portability
@cpindex Strings, portibility
All strings musts be encoded in UTF-8 without any
NUL-character unless express permission is given.
NUL-character may be encoded either using a zero byte
or using Modified UTF-8, where it is encoded using
two bytes. Which is used is selected in the protocol,
however headers and their values must not include
NUL-characters. No character may be encoded with more
bytes than necessary. Encoding a character in extra
long form is a security issue, and is prune to bugs,
and is hence disallowed by newer specifications of
UTF-8.

@item
@cpindex New line, portability
@cpindex Strings, portibility
The new line-character is always LF (@code{'\n'},
10, line feed) and never a combination of LF and
any other character, or multiple LF:s.
@end itemize



@node Utilities
@chapter Utilities

@menu
* mds-respawn::                     The server immortality protocol.
* mds-reg::                         The registry control command.
* mds-clip::                        The clipboard control command.
* mds-screenshot::                  The screenshot utility.
* mds-slay::                        The process killing utility.
* mds-chvt::                        Utility for switching virtual terminal.
* mds-kbdc::                        The keyboard layout compiler.
* External Utilities::              Suggestion on utilities you can utilise.
@end menu



@node mds-respawn
@section @command{mds-respawn}

@pgindex @command{mds-respawn}
@cpindex Respawning servers, automatic
@cpindex Crash resilience
@command{mds-respawn} is a utility intended to be used
in @file{$@{XDG_CONFIG_HOME@}/mdsinitrc}. It will
spawn a selected set of servers. If a server it
spawns exits with a bad status, @command{mds-respawn}
will respawn it. @command{mds-respawn} supports two
options in the command line:

@table @option
@item --alarm=SECONDS
@opindex @option{--alarm}
Schedule @command{mds-respawn} to die in @var{SECONDS}
seconds. At most 1 minute.

@item --interval=SECONDS
@opindex @option{--interval}
@sgindex @code{SIGUSR2}
Spawned servers that die twice with @var{SECONDS}
seconds should stop respawning until the signal
@code{SIGUSR2} is send to @command{mds-respawn}.
At most 1 minute.
@end table

Commands for servers to spawn are specified within
curly braces. Each of the braces must be alone its
its own argument. For example:

@opindex @option{--initial-spawn}
@example
@group
mds-respawn --interval=5       \
  @{ mds-foo --initial-spawn @}  \
  @{ mds-bar --initial-spawn @}  &
@end group
@end example

@cpindex Server supervision
@cpindex Supervision of servers
@opindex @option{--initial-spawn}
@opindex @option{--respawn}
will spawn and supervise the servers @command{mds-foo}
and @command{mds-bar}. Both spawned with the argument
@option{--initial-spawn}. When a server is respawed
by @command{mds-respawn}, @option{--initial-spawn} in
its argument list will be replaced by
@option{--respawn} to let the server know it is being
respawned.

@sgindex @code{SIGTERM}
A server is considered to exit with a failure status
unless it exits with the return value 0 or is
terminated by the signal @code{SIGTERM}@.



@node mds-reg
@section @command{mds-reg}

@pgindex @command{mds-reg}
@cpindex List protocols
@cpindex Protocols, listing
@cpindex Protocol registry
@cpindex Registry of protocols
@opindex @option{--list}
@opindex @option{--wait}
@command{mds-reg} is a utility that can be used to
list available protocols provided by running servers.
It can also wait for a set of protocols to become
available. To list all available protocols run
@command{mds-reg --list}. And to wait for the
protocol @code{foo} run @command{mds-reg --wait=foo}.
To also wait for the protocol @code{bar} run
@command{mds-reg --wait=foo,bar} or
@command{mds-reg --wait=foo --wait=bar}. Both of
thesestyles can be mixed if you want to wait for
even more protocols.



@node mds-clip
@section @command{mds-clip}

@pgindex @command{mds-clip}
@cpindex Clipboard
@command{mds-clip} is a utility that can be used to
review the clipboards on the display and manipulate
them. @command{mds-clip} recognises the following
options:

@table @option
@item --push
@opindex @option{--push}
Push non-option arguments from the command line into
the clipboard.

@item --expire=SECONDS
@opindex @option{--expire}
@opindex @option{--push}
Can be used with @option{--push}. The clip will not
removed after @var{SECONDS} seconds.

@item --pop
@opindex @option{--pop}
Pop items from the clipboard whose indices are listed
in the command line as non-option arguments. The first
index is 1.

@item --clear
@opindex @option{--clear}
Pop all items in the clipboard.

@item --list
@opindex @option{--list}
List items in the clipboard whose indices are listed
in the command line as non-option arguments. The first
index is 1. If no indicies are specified, all clips
will be listed.

@item --size
@opindex @option{--size}
Print the size of the clipboard, the number of clips
in the clipboard.

@item --capacity
@opindex @option{--capacity}
Print the capacity of the clipboard, the number of
clips the clipboard can hold. If both @option{--size}
and @option{--capacity} is used, the size will be
printed on the first line and the capacity will be
printed on the second line.

@item --resize=CAPACITY
@opindex @option{--resize}
Change the capaciy of the clipboard to @var{CAPACITY}
clips.

@item --stdin
@opindex @option{--stdin}
@opindex @option{--push}
Can be used with @option{--push}. If used, the clip
that should be placed on the top of the clipboard
stack should be read from stdin.

@item --delimiter=DELIMITER
@opindex @option{--delimiter}
@opindex @option{--list}
@opindex @option{--stdin}
Can be used with @option{--stdin} or @option{--list}.
If used with @option{--stdin}, an line containing
only @var{DELIMITER} will delimit two values that
should be placed in the clipboard. If used with
@option{--list}, a line containing only
@var{DELIMITER} will delimit two values in the
output. The default delimiter for @option{--list}
is an empty line.

@item -1
@opindex @option{-1}
Use the primary clipboard, that is, the text copy
clipboard. This is the default clipboard.

@item -2
@opindex @option{-2}
Use the secondary clipboard, that is, the text
selection clipboard.

@item -3
@opindex @option{-3}
Use the tertiary clipboard, that is, the non-text
copy clipboard.
@end table



@node mds-screenshot
@section @command{mds-screenshot}

@pgindex @command{mds-screenshot}
@cpindex Screenshooting
@command{mds-screenshot} is a simple utility, and
reference implementation thereof, that can take a
screeenshot of either the display, a monitor, or a
window with or without its decorating window. It can
also include or exclude the rat cursor or gamma
ramps. @command{mds-screenshot} recognises the
following options:

@table @option
@item --monitor
@opindex @option{--monitor}
Take screenshot of the monitor. The rat will be used
to select monitor.

@item --monitor=WINDOW_ID
@opindex @option{--monitor}
Take screenshot of the monitor whose root window's
window ID is @var{WINDOW_ID} or has another window in
it whose window ID is @var{WINDOW_ID}@.

@item --embed
@opindex @option{--embed}
Take a screenshot of an embedded window. The rat will
be used to select window.

@item --embed=WINDOW_ID
@opindex @option{--monitor}
Take a screenshot of an embedded window whose window
ID is @var{WINDOW_ID}@.

@item --window
@opindex @option{--window}
Take a screenshot a window. The rat will be used to
select window.

@item --window=WINDOW_ID
@opindex @option{--window}
Take a screenshot of a window whose window ID is
@var{WINDOW_ID}@.

@item --decoration
@opindex @option{--decoration}
Include the window's decoration, if used together
with @option{--window}. Ignored if used without
@option{--window}.

@item --cursor
@opindex @option{--cursor}
Include the rat cursor in the screenshot.

@item --gamma
@opindex @option{--gamma}
Include the effects of gamma ramps in the screenshot.

@item --low-gamma=LOW_PRIORITY
@opindex @option{--low-gamma}
Include the effects of gamma ramps with a priority
above @var{LOW_PRIORITY} in the screenshot.

@item --high-gamma=HIGH_PRIORITY
@opindex @option{--high-gamma}
@opindex @option{--low-gamma}
Include the effects of gamma ramps with a priority
below @var{HIGH_PRIORITY} in the screenshot. If used
together with @option{--low-gamma=LOW_PRIORITY},
the range [@var{LOW_PRIORITY}, @var{HIGH_PRIORITY}]
will be used.
@end table

Optionally, you can add a non-option argument that
specifies the pathname of the saved file.

@opindex @option{--window}
@opindex @option{--monitor}
@opindex @option{--embed}
If neither @option{--monitor}, @option{--embed} or
@option{--window} is used, a screenshot will be taked
of the display. That is, all monitors.

@opindex @option{--gamma}
@opindex @option{--low-gamma}
@opindex @option{--high-gamma}
In case of mirrored outputs, one of the potential
outputs will be selected arbitrarily if
@option{--gamma}, @option{--low-gamma} or
@option{--high-gamma} is used. If neither is used,
the screenshot will be identical for all mirrored
outputs.



@node mds-slay
@section @command{mds-slay}

@pgindex @command{mds-slay}
@cpindex Process killing
@cpindex Killing processes
@command{mds-slay} a utility that can be used to
kill a process by it window or identify the window
ID of a window. @command{mds-slay} recognises the
following options:

@table @option
@item --embed
@opindex @option{--embed}
Kill an embedded window. The rat will be used to
select window.

@item --embed=WINDOW_ID
@opindex @option{--embed}
Kill an embedded window whose window ID is
@var{WINDOW_ID}@.

@item --window
@opindex @option{--window}
Kill a window. The rat will be used to select window.

@item --window=WINDOW_ID
@opindex @option{--window}
Kill a window whose window ID is @var{WINDOW_ID}@.

@item --signal=SIGNAL
@opindex @option{--signal}
Send the signal @var{SIGNAL} to the process owning
the selected window.

@item --no-signal
@opindex @option{--no-signal}
Do not send a signal; only identify the window.

@item --keep-cursor
@opindex @option{--keep-cursor}
Do not change the cursor to a kill cursor.

@item --print
@opindex @option{--print}
Print the ID of the selected window.
@end table



@node mds-chvt
@section @command{mds-chvt}

@pgindex @command{mds-chvt}
@pgindex @command{chvt}
@cpindex Virtual terminal, switching
@cpindex Switching virtual terminal
@command{mds-chvt} is a utility similar to the command
@command{chvt} from the @command{kbd} project.
However, @command{mds-chvt} has setuid and therefore
does not require root permissions, but it will only
request a virtual terminal switch if the display
server's virtual terminal is in the foreground.
@command{mds-chvt} recognises the following options:

@table @option
@item --switch=VT
@opindex @option{--switch}
Switch to the virtual terminal with the index
@var{VT}@.
@end table



@node mds-kbdc
@section @command{mds-kbdc}

@pgindex @command{mds-kbdc}
@cpindex Keyboard layouts, compile
@cpindex Compile keyboard layouts
@cpindex Compose tables, compile
@cpindex Compile compose tables
@command{mds-kbdc} is the program used to compile
keyboard layouts and compose tables.

TODO how to use mds-kbdc



@node External Utilities
@section External Utilities

@cpindex Background processes
@opindex @option{--on-init-fork}
@pgindex @file{mdsinitrc}
Servers let you use the option @option{--on-init-fork}
to put the process in the background when it has been
initialised. This can used to spawn that depend on
each other in linear order. For example, if
@command{mds-bar} requires that @command{mds-foo} is
initialised before it can be initialised, you can in
@file{$@{XDG_CONFIG_HOME@}/mdsinitrc} write:

@example
@group
mds-foo --on-init-fork
mds-bar &
@end group
@end example

@opindex @option{--on-init-fork}
@opindex @option{--on-init-sh}
@pgindex @command{mds-respawn}
@pgindex @command{cmdipc}
@pgindex @command{ipcmd}
This will start @command{mds-bar} when
@command{mds-foo} has been initialised. However if
one of them crashes, that server will not respawn; to
fix this @command{mds-respawn} can be used, but use
of @command{mds-respawn} hinders the use of
@option{--on-init-fork}. Instead you can use
@option{--on-init-sh} and global semaphores. The
packages, and commands, @command{cmdipc} and
@command{ipcmd} can be used for this purpose. We will
use @command{cmdipc} in an example:

@ifset AFOURPAPER
@example
S=$(cmdipc -Scx set 1 | cut -d ' ' -f 2)
# Create a System V semaphore with the value 1.

mds-respawn @{ mds-foo --on-init-sh="cmdipc -Sk $S p" @} &
# Spawn `mds-foo` and decrease the semaphore with 1 when initialised.

cmdipc -Sk $S z            # Wait for the semaphore's value to become 0.
cmdipc -Srk $S             # Remove the semaphore.
mds-respawn @{ mds-bar @} &  # Spawn `mds-bar`.
@end example
@end ifset
@ifclear AFOURPAPER
@ifset USLETTER
@example
S=$(cmdipc -Scx set 1 | cut -d ' ' -f 2)
# Create a System V semaphore with the value 1.

mds-respawn @{ mds-foo --on-init-sh="cmdipc -Sk $S p" @} &
# Spawn `mds-foo` and decrease the semaphore with 1 when initialised.

cmdipc -Sk $S z            # Wait for the semaphore's
                           # value to become 0.
cmdipc -Srk $S             # Remove the semaphore.
mds-respawn @{ mds-bar @} &  # Spawn `mds-bar`.
@end example
@end ifset
@ifclear USLETTER
@example
S=$(cmdipc -Scx set 1 | cut -d ' ' -f 2)
# Create a System V semaphore with the value 1.

mds-respawn @{ mds-foo --on-init-sh="cmdipc -Sk $S p" @} &
# Spawn `mds-foo` and decrease the semaphore with
# 1 when initialised.

cmdipc -Sk $S z            # Wait for the semaphore's
                           # value to become 0.
cmdipc -Srk $S             # Remove the semaphore.
mds-respawn @{ mds-bar @} &  # Spawn `mds-bar`.
@end example
@end ifclear
@end ifclear

@pgindex @command{mds-reg}
This is however seldom necessary as @command{mds-reg}
can often be used instead, with more abstraction as
you would only need to specify what servers need to
wait for, not what they provide.

@pgindex @command{setpgrp}
@cpindex Display server process group
@cpindex Process group, display server
Another useful command (and package) is
@command{setpgrp}. @command{mds} puts itself an all
its children in a new process group. However you may
want to put processes that are not @command{mds}
servers or @command{mds} utilities in a separate
process group. @command{setpgrp} can be used to start
a process in a new process group.



@node Servers
@chapter Servers

@pgindex @command{mds}
@pgindex @command{mds-server}
@cpindex Kernel
@cpindex Display server kernel
@cpindex Master server
An @command{mds} display server instance is comprised
of multiple small servers that each implements a
small part of the display server's functionallity.
This chapter will include all servers but the master
server, @command{mds-server} and the kernel,
@command{mds}, the latter of which is not actually a
server.

@menu
* mds-echo::                        The @command{mds-echo} server.
* mds-registry::                    The @command{mds-registry} server.
* mds-vt::                          The @command{mds-vt} server.
* mds-clipboard::                   The @command{mds-clipboard} server.
* mds-drag::                        The @command{mds-drag} server.
* mds-kkbd::                        The @command{mds-kkbd} server.
* mds-kkbdrate::                    The @command{mds-kkbdrate} server.
* mds-kbd::                         The @command{mds-kbd} server.
* mds-keytrans::                    The @command{mds-keytrans} server.
* mds-keystick::                    The @command{mds-keystick} server.
* mds-keybounce::                   The @command{mds-keybounce} server.
* mds-slowkey::                     The @command{mds-slowkey} server.
* mds-keycue::                      The @command{mds-keycue} server.
* mds-kbdbind::                     The @command{mds-kbdbind} server.
* mds-multikey::                    The @command{mds-multikey} server.
* mds-rat::                         The @command{mds-rat} server.
* mds-ratbarrier::                  The @command{mds-ratbarrier} server.
* mds-ratbind::                     The @command{mds-ratbind} server.
* mds-gestures::                    The @command{mds-gestures} server.
* mds-kbd2rat::                     The @command{mds-kbd2rat} server.
* mds-hwcursor::                    The @command{mds-hwcursor} server.
* mds-swcursor::                    The @command{mds-swcursor} server.
* mds-cursorshadow::                The @command{mds-cursorshadow} server.
* mds-cursorgamma::                 The @command{mds-cursorgamma} server.
* mds-hwgamma::                     The @command{mds-hwgamma} server.
* mds-swgamma::                     The @command{mds-swgamma} server.
* mds-coopgamma::                   The @command{mds-coopgamma} server.
* mds-dcvs::                        The @command{mds-dcvs} server.
* mds-colour::                      The @command{mds-colour} server.
* mds-retro-crt::                   The @command{mds-retro-crt} server.
* mds-state::                       The @command{mds-state} server.
* mds-focus::                       The @command{mds-focus} server.
* mds-kill::                        The @command{mds-kill} server.
* mds-screensaver::                 The @command{mds-screensaver} server.
* mds-compositor::                  The @command{mds-compositor} server.
* mds-crtc::                        The @command{mds-crtc} server.
* mds-dri::                         The @command{mds-dri} server.
* mds-fb::                          The @command{mds-fb} server.
* mds-mds::                         The @command{mds-mds} server.
* mds-meta::                        The @command{mds-meta} server.
* mds-seat::                        The @command{mds-seat} server.
* mds-nest::                        The @command{mds-nest} server.
* mds-host::                        The @command{mds-host} server.
* mds-remote::                      The @command{mds-remote} server.
* mds-xmds::                        The @command{mds-xmds} server.
* mds-wmds::                        The @command{mds-wmds} server.
* mds-mmds::                        The @command{mds-mmds} server.
* mds-mdsx::                        The @command{mds-mdsx} server.
* mds-mdsw::                        The @command{mds-mdsw} server.
* mds-mdsm::                        The @command{mds-mdsm} server.
* mds-posmem::                      The @command{mds-posmem} server.
* mds-decorator::                   The @command{mds-decorator} server.
* mds-tile::                        The @command{mds-tile} server.
* mds-stack::                       The @command{mds-stack} server.
* mds-desktop::                     The @command{mds-desktop} server.
* mds-workspace::                   The @command{mds-workspace} server.
* mds-tray::                        The @command{mds-tray} server.
@end menu



@node mds-echo
@section @command{mds-echo}

@pgindex @command{mds-echo}
@cpindex Ping
@cpindex Debugging
@cpindex Heartbeat
@cpindex Network heartbeat
@command{mds-echo} is a server that echos message
that contain the header--value pair
@code{Command: echo}. This server can be used for
debugging and testing as well as to enable network
heartbeats.



@node mds-registry
@section @command{mds-registry}

@pgindex @command{mds-registry}
@cpindex List protocols
@cpindex Protocols, listing
@cpindex Protocol registry
@cpindex Registry of protocols
@command{mds-registry} is a server that keeps a
registry of all protocols that are supported they the
sum of all active servers. It can also be used by
other servers to wait until a protocol has become
available.



@node mds-vt
@section @command{mds-vt}

@pgindex @command{mds-vt}
@cpindex Virtual terminal, switching
@cpindex Virtual terminal, mode switching
@cpindex Switching virtual terminal
@cpindex Switching virtual terminal mode
@cpindex TTY
@cpindex Graphical mode
@cpindex Text mode
@cpindex Mode, virtual terminal, switching
@command{mds-vt} is the server that acquires a virtual
terminal for the display, manages virtual terminal
switches and enables other servers to get access to
the virtual terminal's TTY and informs them of which
virtual terminal the display is located on. It also
enables other servers to switch the virtual terminals
mode to graphical mode or text mode.

@vrindex @env{XDG_VTNR}
@pgindex @command{mds-vt}
@pgindex @file{mdsinitrc}
By default @command{mds-vt} will select the next
available virtual terminal for the display server.
You can override this behaviour by exporting a value
to the environment variable @env{XDG_VTNR}@. The value
must be a decimal integer of a valid virtual terminal
index@footnote{Which is the same thing as a valid TTY
index.}. To select the virtual terminal the display
was started from you can use the following code in
your @file{~/.mdsinitrc}:

@pgindex @command{fgconsole}
@example
export XDG_VTNR="$(fgconsole)"
@end example

@pgindex @command{kbd}
@command{fgconsole} is a part of the @command{kbd}
package.



@node mds-clipboard
@section @command{mds-clipboard}

@pgindex @command{mds-clipboard}
@cpindex Clipboard
@command{mds} has three clipboards, one for copied
text, one for selected text, and one for non-textual
data. Each of these clipboards are stacks, just like
in GNU Emacs. @command{mds-clipboard} implements
these clipboards and automatic removal of outdated
clips. Clips can be configured to expire based on
time or when its originator closes.



@node mds-drag
@section @command{mds-drag}

@pgindex @command{mds-drag}
@cpindex Drag-and-drop
@command{mds-drag} is the server that implements
drag-and-drop support.



@node mds-kkbd
@section @command{mds-kkbd}

@pgindex @command{mds-kkbd}
@cpindex Keyboard
@cpindex Keyboard, kernel-based
@cpindex Scancodes
@cpindex Keycodes
@cpindex Keycodes, remapping
@cpindex Keyboard, remapping
@command{mds-kkbd} implements access to the
kernel-based keyboard. It does not however implement
delay and rate configurations for the kernel-based
keyboard as that requires root privileges. The
kernel-based keyboard is a keyboard that can be
accessed by reconfiguring stdin in a TTY using
@code{ioctl} and then read from stdin.
@command{mds-kkbd} does not implement any keyboard
layout, rather it broadcasts scancodes and keycodes.
However it can remap keycodes, but not scancodes.



@node mds-kkbdrate
@section @command{mds-kkbdrate}

@pgindex @command{mds-kkbdrate}
@pgindex @command{mds-kkbd}
@cpindex Keyboard
@cpindex Keyboard, kernel-based
@cpindex Keyboard repeat rate
@cpindex Keyboard repeat delay
@command{mds-kkbdrate} is a complemental server to
@command{mds-kkbd}, it implements rate and delay
control for the kernel-based keyboard.



@node mds-kbd
@section @command{mds-kbd}

@pgindex @command{mds-kbd}
@cpindex Keyboard
@cpindex Keyboard repeat rate
@cpindex Keyboard repeat delay
@cpindex Scancodes
@cpindex Keycodes
@cpindex Keycodes, remapping
@cpindex Keyboard, remapping
@command{mds-kbd} is an alternative to
@command{mds-kkbd} and @command{mds-kkbdrate}.
In contrast to @command{mds-kkbd}, @command{mds-kbd}
implements control over individual keybroads rather
than utilising the kernels keyboard drivers to treats
all keyboards a one keyboard. This server is only
useful for multiseat sessions and if you otherwise
actually want to handle the keyboards individually.



@node mds-keytrans
@section @command{mds-keytrans}

@pgindex @command{mds-keytrans}
@pgindex @command{mds-kbd}
@pgindex @command{mds-kkbd}
@cpindex Keyboard layout
@cpindex Layout, keyboard
@cpindex Dead keys
@cpindex Compose key
@cpindex Modifier keys
@cpindex Keys, mapping, layout
@cpindex Keys, dead
@cpindex Keys, compose
@cpindex Keys, modifiers
@command{mds-keytrans} is the server than translates
keycodes from @command{mds-kkbd} and
@command{mds-kbd}, and third-party alternatives, to
characters and other attributes. It implements the
keyboard's layouts including modifiers, letters,
other symbols, dead keys and compose.



@node mds-keystick
@section @command{mds-keystick}

@pgindex @command{mds-keystick}
@cpindex Sticky keys
@cpindex Keyboard, accessibility
@cpindex Accessibility, keyboard
@command{mds-keystick} is a server that can be used
to enable sticky keys. See @ref{Sticky Keys} for more
information.



@node mds-keybounce
@section @command{mds-keybounce}

@pgindex @command{mds-keybounce}
@cpindex Bounce keys
@cpindex Keyboard, accessibility
@cpindex Accessibility, keyboard
@command{mds-keybounce} is a server that can be used
to enable bounce keys. See @ref{Bounce Keys} for more
information.



@node mds-slowkey
@section @command{mds-slowkey}

@pgindex @command{mds-slowkey}
@cpindex Slow keys
@cpindex Keyboard, accessibility
@cpindex Accessibility, keyboard
@command{mds-slowkey} is a server that can be used
to enable slow keys. See @ref{Slow Keys} for more
information.



@node mds-keycue
@section @command{mds-keycue}

@pgindex @command{mds-keycue}
@cpindex Loud keys
@cpindex Keyboard, accessibility
@cpindex Accessibility, keyboard
@command{mds-keycue} is a server that can be used
to enable loud keys. See @ref{Loud Keys} for more
information.



@node mds-kbdbind
@section @command{mds-kbdbind}

@pgindex @command{mds-kbdbind}
@pgindex @command{xbindkeys}
@pgindex @command{dmenu}
@cpindex Hotkeys
@cpindex Keyboard bindings
@cpindex Bindings, keyboard
@cpindex Layout, keyboard, switching
@cpindex Keyboard layout, switching
@cpindex Switching keyboard layout
@command{mds-kbdbind} is a server similar to
@command{xbindkeys}. It can be used to run commands
upon selected key combinations, for example starting
@command{dmenu} or change keyboard layout.
@command{mds-kbdbind} can distinguish keyboards
from each other.



@node mds-multikey
@section @command{mds-multikey}

@pgindex @command{mds-multikey}
@pgindex @command{mds-kbdbind}
@cpindex Keyboard bindings
@cpindex Bindings, keyboard
@command{mds-multikey} is a server that can bind a
key, key combination, or sequence their of to a
sequence of keys or key combinations. For example,
you could bind @kbd{<super>x, y} to simulate that a
key @key{Faux1} is pressed, a key that does not
exist, this key press could be picked up by
@command{mds-kbdbind} to enable @command{mds-kbdbind}
to respond to squences rather than single keys and
single key combinations. alternatively you could bind
@kbd{<super>x} to press @key{x} a selected number of
times with a short selectable delay between them; or
@kbd{<super>x, 5'} to press @key{x} five times.



@node mds-rat
@section @command{mds-rat}

@pgindex @command{mds-rat}
@cpindex Rat device
@cpindex Mouse device
@cpindex Pointing device
@command{mds-rat} is a server that implements support
of rat (also known as mouse) devices.



@node mds-ratbarrier
@section @command{mds-ratbarrier}

@pgindex @command{mds-ratbarrier}
@cpindex Cursor barriers
@cpindex Rat pointer barriers
@cpindex Mouse pointer barriers
@cpindex Pointer barriers
@cpindex Screen edges, barriers
@cpindex Barriers, rat
@command{mds-ratbarrier} is a server that lets you
set up barriers for the rat pointer, for example at
the screen edges.

A barrier requires that the rat be moved a bit extra
move it can move on to the next pixel. A barrier can
be directional. A barrier can also be infinite, which
blocks the rat pointer fully and it cannot pass
through at all.



@node mds-ratbind
@section @command{mds-ratbind}

@pgindex @command{mds-ratbind}
@cpindex Bindings, rat
@cpindex Rat bindings
@cpindex Mouse bindings
@cpindex Pointer bindings
@cpindex Hotcorners
@command{mds-ratbind} is a server similar to
@command{mds-kbdbind}. However, @command{mds-ratbind}
respons to rat and rat cursor actions rather than
keyboard actions. It can for example be used to
implement hotcorners.



@node mds-gestures
@section @command{mds-gestures}

@pgindex @command{mds-gestures}
@cpindex Bindings, gestures
@cpindex Gestures bindings
@cpindex Rat gestures bindings
@cpindex Mouse gestures bindings
@cpindex Pointer gestures bindings
@command{mds-gestures} is a server similar to
@command{mds-ratbind}. However it is specialised to
respond to gestures.



@node mds-kbd2rat
@section @command{mds-kbd2rat}

@pgindex @command{mds-kbd2rat}
@cpindex Keyboard to rat bindings
@cpindex Rat keys
@cpindex Mouse keys
If you do not have a rat or rather use your keyboard,
the server @command{mds-kbd2rat} can be used to bind
keyboard actions to simulate rat actions. This server
is a specialisation of @code{mds-kbdbind}, rather
than spawning generic commands it broadcasts messages
within the display server to move the rat cursor and
click on rat buttons. @code{mds-kbdbind} could be
used to do this, but @command{mds-kbd2rat} will not
spawn a new process for each action. For more
information see @ref{Mouse Keys}.



@node mds-hwcursor
@section @command{mds-hwcursor}

@pgindex @command{mds-hwcursor}
@cpindex Cursor, hardware
@cpindex Rat cursor, hardware
@cpindex Mouse cursor, hardware
@cpindex Hardware cursor
@command{mds-hwcursor} is a server that draws the rat
cursor to the monitor on a plane separate from all
other content on the display. In less esoteric terms,
it implements a hardware cursor.



@node mds-swcursor
@section @command{mds-swcursor}

@pgindex @command{mds-swcursor}
@cpindex Cursor, software
@cpindex Rat cursor, software
@cpindex Mouse cursor, software
@cpindex Software cursor
@command{mds-swcursor} is a server that draws the rat
cursor to the monitor on the same plane as all other
content on the display. In less esoteric terms, it
implements a software cursor.



@node mds-cursorshadow
@section @command{mds-cursorshadow}

@pgindex @command{mds-cursorshadow}
@cpindex Cursor shadow
@cpindex Rat cursor shadow
@cpindex Mouse cursor shadow
@cpindex Shadow, cursor
@command{mds-cursorshadow} is a server that can be
used to decorate the rat cursor with a configurable
shadow.



@node mds-cursorgamma
@section @command{mds-cursorgamma}

@pgindex @command{mds-cursorgamma}
@pgindex @command{mds-hwcursor}
@cpindex Gamma correction, hardware cursor
@cpindex Cursor, hardware, gamma correction
@cpindex Rat cursor, hardware, gamma correction
@cpindex Mouse cursor, hardware, gamma correction
@cpindex Hardware cursor, gamma correction
@cpindex Graphics drivers
@command{mds-cursorgamma} is a server you can use if
you use @command{mds-hwcursor} to, if not done by the
graphics driver, correct the gamma correction on the
hardware cursor using software gamma ramps. This of
courses works whether you are using hardware or
software gamma ramps for your monitor's gamma
correction. If can even be used if you do not use
gamma correction, in such case, only the cursor will
have its gamma corrected.



@node mds-hwgamma
@section @command{mds-hwgamma}

@pgindex @command{mds-hwgamma}
@cpindex Gamma correction, hardware
@cpindex Hardware gamma correction
To enable gamma correction, use the server
@command{mds-hwgamma}. It implements hardware gamma
ramps, that is, gamma ramps assisted by hardware
acceleration.



@node mds-swgamma
@section @command{mds-swgamma}

@pgindex @command{mds-swgamma}
@cpindex Gamma correction, software
@cpindex Software gamma correction
@cpindex Graphics drivers
If your graphics driver does not support
@command{mds-hwgamma}, you can instead use
@command{mds-swgamma}. It implements software gamma
ramps, that is, it will modify each pixel according
to the selected gamma correction before it is send
to the presentation sever. To accelerate this process,
@command{mds-swgamma} can tell programs how to modify
its colours before sending it; the programs can then
tell @command{mds-swgamma} not to apply its
correction. Programs such as video players can also
use this to tell the server not to apply gamma
correction as that may cause the video to be played
back to slowly.



@node mds-coopgamma
@section @command{mds-coopgamma}

@pgindex @command{mds-coopgamma}
@cpindex Gamma correction, cooperative
@cpindex Gamma correction, chain
@cpindex Gamma correction, filters
@cpindex Cooperative gamma correction
@command{mds-coopgamma} is a server that
can be used to enable multiple clients to manipulate
the gamma ramps without stepping on each others toes.
It does this by letting clients tell which priority
their corrections has and use this data to chain
together there modifications. For example if one
program wants to apply a red filter to the display
and another program wants to correct the monitors'
gamma, the red filter program will send lookup tables
for the gamma with high priority and the correction
program will send its lookup tables with low priority.
@command{mds-coopgamma} will then apply the latter
lookup tables on top of the red filter. The clients
can tell @command{mds-coopgamma} whether it should
remove their changes when they close, or even keep
them and wait for the client to restart.



@node mds-dcvs
@section @command{mds-dcvs}

@pgindex @command{mds-dcvs}
@cpindex Defective colour vision, simulation
@cpindex Simulateion of defective colour vision
@cpindex Colour blindness, simulation
@cpindex Simulateion of colour blindnes
@command{mds-dcvs} is a server than can be used to
simulate defective colour vision. That is, it can for
example turn the display greyscale (colour blindness)
or add a filter the simulates deuteranopia or
deuteranomaly. This server is intended for testing
that interfaces are suitable for people with
defective colour vision.



@node mds-colour
@section @command{mds-colour}

@pgindex @command{mds-colour}
@cpindex Colour names
@cpindex System colours
@cpindex Colours, system
@cpindex Colours, names
@command{mds-colour} is a server that implements
colour names, such as system colours and generic
names, for example `red', whose exact colour can be
configured by the user. A terminal written for
@command{mds} would look up colours such as `red'
and `light red' and get the colours the terminal
should use by default. Nothing is to be assumed
for such colours, not even that `light red' is in
fact lighter than `dark red', or that `red' is in
fact `red', only that it is the colour the user
wants to see when a colour is supposed to be `red'.
@command{mds-colour} will notify clients when a
colour has been reconfigured, added or removed.

@cpindex Colour dithering
@cpindex Dithering of colours
@command{mds-colour} is also responsible for
informing clients on which two colours clients
should use and how to dither them (by percent, not
by pattern). This is useful if only 16-bit colours
can be used, or if only 24-colour can used but
gradients between for example sRGB(255, 255, 255)
and sRGB(254, 254, 254) is to be drawn.

@cpindex Gamma correction, dithering
@command{mds-colour} is gamma ramp-aware. For
example, if for the red channel, 0 is mapped to 0, 1
is mapped to 3, 2 is mapped 2 and 3 is mapped to 1,
but 1 and 3 requires dithering, then if 3 is
requested, @command{mds-colour} will tell the client
to dither 0 and 2 with 50 %, which should generate 1,
but 1 and 3 has been swapped.



@node mds-retro-crt
@section @command{mds-retro-crt}

@pgindex @command{mds-retro-crt}
@pgindex @command{cool-retro-crt}
@command{mds-retro-crt} is a server that applies
filters used in the terminal emulator
@command{cool-retro-term} to the whole display.



@node mds-state
@section @command{mds-state}

@pgindex @command{mds-state}
@cpindex State, windows
@cpindex Windows states
@command{mds-state} is the server that keeps tracks
of the windows' state.



@node mds-focus
@section @command{mds-focus}

@pgindex @command{mds-focus}
@cpindex Window focus
@cpindex Focus of windows and components
@command{mds-focus} is the server focuses windows
and windows' components.



@node mds-kill
@section @command{mds-kill}

@pgindex @command{mds-kill}
@cpindex Signals, sending
@cpindex Process identification
@cpindex Identification of processes
@command{mds-kill} is a server that can be used to
send signals to processes by identifying them by
their windows. This server can also be used to simply
identify the process that owns a window.



@node mds-screensaver
@section @command{mds-screensaver}

@pgindex @command{mds-screensaver}
@cpindex Screensaver
@cpindex Monitor deactivation
@cpindex Deactive monitors
@command{mds-screensaver} is a server that can be
used to start a screensaver or deactive monitors when
the input devices has not be used for a period of
time provided that no client has disabled this. It is
capable of deactiving single monitors or start a
screensaver on single monitors rather than all
monitors.



@node mds-compositor
@section @command{mds-compositor}

@pgindex @command{mds-compositor}
@pgindex @command{mds-dri}
@pgindex @command{mds-fb}
@cpindex Compositor
@cpindex Presentation
@command{mds-compositor} is the server that composes
the output. It takes output of all windows and
arranges it to one image per monitor and sends it to
the presentation servers, such as @command{mds-dri}
and @command{mds-fb}.



@node mds-crtc
@section @command{mds-crtc}

@pgindex @command{mds-crtc}
@cpindex CRTC
@cpindex Cathode ray tube controller
@command{mds-crtc} is the server that identifies
CRTC:s and provide access to them.



@node mds-dri
@section @command{mds-dri}

@pgindex @command{mds-dri}
@cpindex Direct Rendering Infrastructure
@cpindex Presentation
@cpindex Display of content
@cpindex Content, display
@command{mds-dri} is a server that displays
content using the Direct Rendering Infrastructure.



@node mds-fb
@section @command{mds-fb}

@pgindex @command{mds-fb}
@cpindex Framebuffer
@cpindex Presentation
@cpindex Display of content
@cpindex Content, display
@command{mds-fb} is a server that displays content
using framebuffers.



@node mds-mds
@section @command{mds-mds}

@pgindex @command{mds-mds}
@cpindex Monitor emulation
@cpindex Emulation, monitor
@command{mds-mds} is a server that displays
content using another @command{mds} window. It
creates a window that emulates a monitor.



@node mds-meta
@section @command{mds-meta}

@pgindex @command{mds-meta}
@cpindex Metadisplay server
@vrindex @env{MDS_DISPLAY}
@cpindex Server sharing
@cpindex Sharing, servers
@command{mds-meta} is a metadisplay server.
It creates or joins a named metadisplay server,
and creates an alternative value for
@env{MDS_DISPLAY}@. Any server connecting to this
alternative @env{MDS_DISPLAY} connects to this
metadisplay server. This can be used to make servers
shared between display server instances.

@command{mds-meta} uses the environment variable
@env{MDS_METADISPLAY} to acquire the name of the
metadisplay server instance it should join or create.
If @env{MDS_METADISPLAY} has not been set it is
treated as having an empty string for its value which
is a valid metadisplay server instance name.

@command{mds-meta} works by connecting to the running
display server instance, the display, and create a
new display server instance, the metadisplay.
Messages passed via the metadisplay's socket is
forward to the display, and messages passed to via
the display to @command{mds-meta} is send to the
appropriate server. @command{mds-meta} manages
interception in the same way as @command{mds-server}
and @command{mds-remote}.

@pgindex @file{mdsmetainitrc}
If @command{mds-meta} creates a new metadisplay,
rather than joining an existing metadisplay, it will
spawn @file{~/.mdsmetainitrc} to let you start the
shared servers.

@pgindex @command{mds-host}
@pgindex @command{mds-clipboard}
@pgindex @command{mds-remot}
@cpindex Networking
An interesting property of @command{mds-meta} is that
it can be used to share servers across display
servers on multiple computers. For example, if you
start @command{mds-host} and @command{mds-clipboard}
inside the metadisplay on your central computer,
displays started on other servers can run
@command{mds-remote} to connect to the metadisplay
so that all computers share the same clipboard.
However, this network will be centralised and not
distributed, so it is not perfect.



@node mds-seat
@section @command{mds-seat}

@pgindex @command{mds-seat}
@cpindex Sandboxing, seats
@cpindex Seats
@command{mds-seat} is a server that enables
seat-sandboxing. It can be used to place two users
on the same machine without them interfering with
each others monitors and input devices. Servers
started below @command{mds-seat} become shared and
servers started above @command{mds-seat} become
seat-private. @command{mds-seat} can filter messages
from shared servers so only the appropriate seat
receives them.



@node mds-nest
@section @command{mds-nest}

@pgindex @command{mds-nest}
@cpindex Display server, nesting
@cpindex Nested display server
@command{mds-nest} is a server that creates a new
@command{mds} instance inside another @command{mds}
instance. A display server inside another display
server.



@node mds-host
@section @command{mds-host}

@pgindex @command{mds-host}
@pgindex @command{mds-remote}
@cpindex Networking
@command{mds-host} is a server that enables servers
like @command{mds-remote} running on remote machines
to connect to the local machine and its display
server.



@node mds-remote
@section @command{mds-remote}

@pgindex @command{mds-remote}
@cpindex Networking
@command{mds-remote} is a server that enables you to
connect extend a remote @command{mds} with your local
machine. This can be used to make a display server
instance span multiple computers including its
monitors and input devices.



@node mds-xmds
@section @command{mds-xmds}

@pgindex @command{mds-xmds}
@cpindex Compatibility layer, X.org
@cpindex X.org compatibility layer
@command{mds-xmds} is a server that translates X.org
calls to @command{mds} calls. It can be used to run
X.org-only programs inside @command{mds}.



@node mds-wmds
@section @command{mds-wmds}

@pgindex @command{mds-wmds}
@cpindex Compatibility layer, Wayland
@cpindex Wayland compatibility layer
@command{mds-wmds} is a server that translates
Wayland calls to @command{mds} calls. It can be used
to run Wayland-only programs inside @command{mds}.



@node mds-mmds
@section @command{mds-mmds}

@pgindex @command{mds-mmds}
@cpindex Compatibility layer, Mir
@cpindex Mir compatibility layer
@command{mds-mmds} is a server that translates Mir
calls to @command{mds} calls. It can be used to run
Mir-only programs inside @command{mds}.



@node mds-mdsx
@section @command{mds-mdsx}

@pgindex @command{mds-mdsx}
@cpindex Reverse compatibility layer, X.org
@cpindex X.org reverse compatibility layer
@command{mds-mdsx} is a server that translates
@command{mds} calls to X.org calls. It can be used to
enable @command{mds} specific programs to run inside
the X.org display servers.



@node mds-mdsw
@section @command{mds-mdsw}

@pgindex @command{mds-mdsw}
@cpindex Reverse compatibility layer, Wayland
@cpindex Wayland reverse compatibility layer
@command{mds-mdsw} is a server that translates
@command{mds} calls to Wayland calls. It can be used
to enable @command{mds} specific programs to run
inside the Wayland display servers.



@node mds-mdsm
@section @command{mds-mdsm}

@pgindex @command{mds-mdsm}
@cpindex Reverse compatibility layer, Mir
@cpindex Mir reverse compatibility layer
@command{mds-mdsm} is a server that translates
@command{mds} calls to Mir calls. It can be used
to enable @command{mds} specific programs to run
inside the display server Mir.



@node mds-posmem
@section @command{mds-posmem}

@cpindex Memorisation of size and position
@cpindex Position, memorisation
@cpindex Size, memorisation
@pgindex @command{mds-posmem}
@command{mds-posmem} is a server that remembers where
window's were positioned and their size, and moves
and resizes them accordingly when they are created.



@node mds-decorator
@section @command{mds-decorator}

@pgindex @command{mds-decorator}
@cpindex Client-side decoration
@cpindex Decoration
@command{mds-decorator} is a server that provides a
simple, reference implementation of a, window
decorator. This window decorator should implement
snappy and sticky edges and stacking (the title bars
is split into tabs with different windows that have
been stacked togather.)



@node mds-tile
@section @command{mds-tile}

@pgindex @command{mds-tile}
@cpindex Tiling window manager
@cpindex Window manager, tiling
@command{mds-tile} is a server that provides a
simple, reference implementation of a, tiling window
manager.



@node mds-stack
@section @command{mds-stack}

@pgindex @command{mds-stack}
@cpindex Stacking window manager
@cpindex Window manager, stacking
@command{mds-stack} is a server that provides a
simple, reference implementation of a, stack window
manager.



@node mds-desktop
@section @command{mds-desktop}

@pgindex @command{mds-desktop}
@cpindex Desktop
@command{mds-desktop} is a server that provides a
simple, reference implementation of a, desktop.



@node mds-workspace
@section @command{mds-workspace}

@pgindex @command{mds-workspace}
@cpindex Workspaces
@command{mds-workspace} is a server that provides
simple, reference implementation of, workspaces.



@node mds-tray
@section @command{mds-tray}

@pgindex @command{mds-tray}
@cpindex Status icon tray
@cpindex System tray
@cpindex Tray, status icons
@command{mds-tray} is a server that provides a
simple, reference implementation of a, status icon
tray.



@node Protocols
@chapter Protocols

@menu
* Infrastructure Protocols::        Infrastructure protocols.
* Virtual Terminal Protocols::      Virtual terminal protocols.
* Keyboard Protocols::              Keyboard protocols.
* Clipboard Protocols::             Clipboard protocols.
* Status Icon Protocols::           Status icon protocols.
* Colour Protocols::                Colour protocols.
* Screensaver Protocols::           Screensaver protocols.
* Miscellaneous Protocols::         Miscellaneous protocols.
@end menu



@node Infrastructure Protocols
@section Infrastructure Protocols

@menu
* assign-id::                       Assign new ID to client, or fetch current ID@.
* intercept::                       Sign up for reception of message.
* register::                        Register availability of a command for which you implement a service.
* reregister::                      Request for reregistration for available commands.
* error::                           Notify a client about a request failure.
@end menu



@node assign-id
@subsection @code{assign-id}
@prindex @code{assign-id}

@table @asis
@item Identifying header:
@code{Command: assign-id}

@item Action:
Assign new ID to client, or fetch current ID@.

@item Purpose:
Assigning ID to clients so server can respond to that
client.

@item Compulsivity:
Manditory, part of the core infrastructure.

@item Reference implementation:
@command{mds-server}
@end table



@node intercept
@subsection @code{intercept}
@prindex @code{intercept}

@table @asis
@item Identifying header:
@code{Command: intercept}

@item Action:
Sign up for reception of message.

@item Optional header: @code{Stop}
Stop reception of messages if the value for the
header @code{Stop} is @code{yes}.

@item Optional header: @code{Priority}
Signed 64-bit integer of reception priority (reversed
of order.)

@item Optional header: @code{Modifying}
Send message asynchronously and await modification if
the value for the header @code{Modifying} is
@code{yes}.

@item Optional header: @code{Length}
Length of the message.

@item Message:
List of headers and header--value-pairs that
qualifies a message for reception, all messages
qualifies if this list is empty.

@item Purpose:
Filter received message for clients and servers.

@item Purpose:
Assigned interception order for modification of
messages.

@item Compulsivity:
Manditory, part of the core infrastructure.

@item Reference implementation:
@command{mds-server}
@end table



@node register
@subsection @code{register}
@prindex @code{register}

@table @asis
@item Identifying header:
@code{Command: register}

@item Action:
Register availability of a command for which you
implement a service.

@item Required header: @code{Client ID}
Your ID, provided by the @code{ID assignment}-header in
response to a @code{Command: assign-id}-header.

@item Conditionally required header: @code{Length}
Length of the message.
Required if @code{Action: list} is included in the
headers.

@item Optional header: @code{Action}
@table @code
@item remove
Remove availability from registry if the value of the
header @code{Action} is @code{remove}.
@item wait
Wait until listed commands are available if the value
of the header @code{Action} is @code{wait}. However
if a protocol becomes unavailable during this wait
period it will still be counted as available for this
wait action.
@item list
Send a list of availability commands if the value of
the header @code{Action} is @code{list}.
@end table

@item Conditionally optional header: @code{Time to live}
The maximum number of seconds to wait. Available and
optional if @code{Action: wait} is included in the
headers.

@item Message:
List of values for the header @code{Command} that you
implement.

@item Purpose:
Identify supported display server operations.

@item Purpose:
Initialisation process synchronisation.

@item Compulsivity:
Highly recommended, programs may stall a bit from
time to time without it, or at initialisation
depending on the program's implementation.

@item Reference implementation:
@command{mds-registry}
@end table



@node reregister
@subsection @code{reregister}
@prindex @code{reregister}

@table @asis
@item Identifying header:
@code{Command: reregister}

@item Action:
Request that all servers resends
@code{Command: register} with either @code{Action: add}
or without the @code{Action}-header (does the same
thing.)

@item Purpose:
Rebuild registry created with @code{Command: register}
if the registry server crashes.

@item Compulsivity:
Highly recommended, programs may think a protocol is
not supported of the registry server crashes if you
do not implement this in your server.

@item Reference implementation:
@command{mds-registry}.
@end table



@node error
@subsection @code{error}
@prindex @code{error}

@table @asis
@item Identifying header:
@code{Command: error}

@item Action:
Notify a client about a request failure.

@item Required header: @code{To}
The ID of the client that send a request that failed.

@item Required header: @code{In response to}
The ID of the message whose request failed.

@item Required header: @code{Error}
The errno number of the error, 0 on success if the
message was not an information query. The string
``custom'' can be used if there is not errno number,
optionally followed by a blank space and a number
that identifies the error, this number must be
positive (not zero).

@item Conditionally optional header: @code{Length}
The length of the message.
Available and optional if ``custom'' is used in the
header @code{Error}.

@item Message:
Description of the error, single line, mid-sentence
case, no punctuation in the end, must not be question
but rather it must be a statement.

@item Purpose:
Enable keyboard layout servers to automatically set
active locks when the server starts based on
currently active LED:s.

@item Compulsivity:
Optional.
@end table



@node Virtual Terminal Protocols
@section Virtual Terminal Protocols

@menu
* get-vt::                          Get the index of the virtual terminal the server is display on.
* configure-vt::                    Reconfigure the virtual terminal the server is display on.
* switching-vt::                    Notify servers about an ongoing virtual terminal switch.
@end menu



@node get-vt
@subsection @code{get-vt}
@prindex @code{get-vt}

@table @asis
@item Identifying header:
@code{Command: get-vt}

@item Action:
Get the index of the virtual terminal the server is
display on.

@item Required header: @code{Client ID}
Your ID, provided by the @code{ID assignment}-header in
response to a @code{Command: assign-id}-header.

@item Response:
The server will response with the header
@code{VT index} and the index of the virtual terminal
the server is display on in decimal format.
Additionally the server will respond with the header
@code{Active} with the value @code{yes} if the VT is
in the foreground or the value @code{no} if the VT is
in the background.

@item Purpose:
Allow programs to be aware of whether the display is
in the foreground or the background.

@item Purpose:
Allow programs to be aware of which VT the server is
running on.

@item Purpose:
Allow programs to gain access of the TTY associated
with the VT such that they can use ioctl and similar
calls on that TTY@.

@item Compulsivity:
Required.

@item Reference implementation:
@code{mds-vt}
@end table



@node configure-vt
@subsection @code{configure-vt}
@prindex @code{configure-vt}

@table @asis
@item Identifying header:
@code{configure-vt}

@item Action:
Reconfigure the virtual terminal the server is
display on.

@item Required header: @code{Client ID}
Your ID, provided by the @code{ID assignment}-header in
response to a @code{Command: assign-id}-header.

@item Optional header: @code{Graphical}
@table @code
@item yes
Set the TTY graphical mode if the value of the header
@code{Graphical} is @code{yes}.
@item no
Set the TTY text mode if the value of the header
@code{Graphical} is @code{no}.
@end table
The server implementing this protocol should not set
the TTY to text mode temporarily when switching TTY@.
It is up to the server that set the request for
graphical mode to temporarily switch to text mode
when switching TTY@.

@item Optional header: @code{Exclusive}
@table @code
@item yes
The server may block other process from opening the
TTY if the value of the header @code{Exclusive} is
@code{yes}.
@item no
The server may not block other process from opening
the TTY if the value of the header @code{Exclusive}
is @code{no}.
@end table
The server implementing this protocol should keep a
counter for how many servers have requested
non-exclusive mode and only switch back to exclusive
mode when that counter reaches zero

@item Response:
The server will response with a @code{Command: error}.

@item Purpose:
Allow presentation servers to enter and leave
graphical mode.

@item Purpose:
Allow programs to gain access of the TTY associated
with the VT such that they can use ioctl and similar
calls on that TTY@.

@item Compulsivity:
Required.

@item Reference implementation:
@code{mds-vt}
@end table



@node switching-vt
@subsection @code{switching-vt}
@prindex @code{switching-vt}

@table @asis
@item Identifying header:
@code{Command: switching-vt}

@item Action:
Notify servers about an ongoing virtual terminal
switch.

@item Required header: @code{Status}
@table @code
@item deactivating
The kernel wants to place the display in the
background if the value of the header @code{Status}
is @code{deactivating}.
@item activating
The kernel wants to place the display in the
foreground if the value of the header @code{Status}
is @code{activating}.
@end table

@item Instructions:
When a virtual terminal switch is requested the
server implementing control VT switching involving
the display's virtual terminal will get signaled by
the kernel. Upon this signal the server should
broadcast this command. All servers that need to
release or acquire resouces should intercept this
message with the possibility of modifying it. Once a
server is ready for the VT to switch it should let
the message pass to the next server by telling the
master server that it is no modification to do. Once
all servers are read for the switch the server that
emitted this message should signal the kernel that it
may switch VT@. The server should detect this by
setting up secondary contection to the display that
intercepts this message. This connection should
intercept this message with priority @math{-2^{62}},
all servers that need to perform actions before the
switch takes place must have a priority higher than
@math{-2^{62}}, preferably 0.

@item Purpose:
Allow servers to release resources when the user
switch virtual terminal before the terminal actually
changes and to reacquire resources when the virtual
terminal become active again.

@item Compulsivity:
Required.

@item Reference implementation:
@code{mds-vt}
@end table



@node Keyboard Protocols
@section Keyboard Protocols

@menu
* key-sent::                        Announce a keyboard input event.
* enumerate-keyboards::             List available keyboards.
* keyboard-enumeration::            Response to @code{Command: enumerate-keyboards}.
* set-keyboard-leds::               Activate and deactivate LED:s on a keyboard.
* get-keyboard-leds::               List exisiting LED:s on a keyboard and their state.
* set-keyboard-rate::               Set the repeat rate and repeat delay on a keyboard.
* get-keyboard-rate::               Get the repeat rate and repeat delay on a keyboard.
* keycode-map::                     Remap keyboard keycodes and query current mapping.
* new-keyboard::                    Announce the existance of a new keyboard.
* old-keyboard::                    Announce the removal of an old keyboard.
@end menu



@node key-sent
@subsection @code{key-sent}
@prindex @code{key-sent}

@table @asis
@item Identifying header:
@code{Command: key-sent}

@item Action:
Announce a keyboard input event.

@item Required header: @code{Keyboard}
Any string that uniquely identifies the keyboard.
@table @asis
@item Purpose:
Enable multi-keyboard aware programs and give at
least on keyboard per seat in a multi-seat
environment.
@item Note:
mds-kkbd uses @code{kernel} to indicate that it uses
the kernel and thus lumps together all keyboards.
@end table

@item Required header: @code{Released}
@table @code
@item yes
The value of the header @code{Released} will be
@code{yes} if the key was released.
@item no
The value of the header @code{Released} will be
@code{no} otherwise, that is, held down or pressed.
@end table
Note: pause/break is automatically released directly
after it has been pressed. This is feature built into
keyboards and servers should not try to circumvent
this.

@item Required header: @code{Keycode}
An unsigned 14-bit integer identifying the key, may
be remapped.

@item Optional header: @code{Scancode}
Either an unsigned 7-bit integer or a single blank
space separated trio of unsigned 7-bit integers,
identifying the key. This is the scancode sent from
the keyboard and optionally unified by the keyboard
driver, however with the typed/released bit zeroed
out. This may not be remapped.

@item Optional header: @code{Modifiers}
Single blank space separated list of active modifiers:
@table @code
@item shift
@key{Shift} (level 2)
@item ctrl
@key{Control}
@item alt
@key{Alternative}/@key{Option}
@item altgr
@key{Alternative Graphic} (level 3)
@item lvl*
@code{*} may be any @math{2^n + 1} integer with
@math{1 < n < 20}.
@item super
@key{Super}
@item hyper
@key{Hyper}
@item ultra
@key{Ultra}
@item caps
@key{Caps} (usually a lock key)
@item num
@key{Num} (usually a lock key)
@item scrl
@key{Scroll} (usually a lock key)
@item top
@key{Top} (historical)
@item front
@key{Front} (historical)
@item greek
@key{Greek} (historical)
@item compose
@key{Compose} (rare, it is usually a dead key)
@end table
Any key that has been locked should be prefix with
@code{+}, if the key has been locked by nullified
with non-lock modifier it should be prefixed with a
@code{-}. If no modifier is active or has been
nullified, @code{none} should be used.

@item Optional header: @code{Key}
A textual representation of the key that has been
typed or released, as mapped by the keyboard layout.
@table @code
@item esc
@key{Escape}
@item f*
@key{F*} where @code{*} is any integer.
@item sysrq
@key{System Request}/@key{Print Screen}
@item scrl
@key{Scroll} (lock)
@item break
@key{Break}/@key{Pause}
@item backspace
@key{Backspace}
@item tab
@key{Tab}
@item return
@key{Return}/@key{Enter}
@item space
@key{Blank Space}
@item menu
@key{Application Menu}
@item ins
@key{Insert}
@item home
@key{Home}
@item pgup
@key{Page Up}
@item del
@key{Delete}
@item end
@key{End}
@item pgdown
@key{Page Down}
@item up
@key{Up} arrow
@item left
@key{Left} arrow
@item down
@key{Down} arrow
@item right
@key{Right} arrow
@item shift
@key{Shift} (level 2)
@item begin
@key{Begin} (keypad @key{5} in nagivation mode)
@item ctrl
@key{Control}
@item alt
@key{Alternative}/@key{Option}
@item altgr
@key{Alternative Graphic} (level 3)
@item lvl*
@code{*} may be any @math{2^n + 1} integer with
@math{1 < n < 20}.
@item super
@key{Super}
@item hyper
@key{Hyper}
@item ultra
@key{Ultra}
@item caps
@key{Caps} (usually a lock key)
@item num
@key{Num} (usually a lock key)
@item scrl
@key{Scroll} (usually a lock key)
@item top
@key{Top} (historical)
@item front
@key{Front} (historical)
@item greek
@key{Greek} (historical)
@item compose
@key{Compose} (usually a dead key)
@item hexcompose
@key{Hex-Compose} (usually a dead key)
(Used to create aribitrary characters.)
@item longhexcompose
@key{Long Hex-Compose} (usually a dead key)
(Variant of @code{hexcompose} for longer codepoints.)
@item modelock
@key{Mode Lock}
@item letter *
@code{*} may be any UTF-8 encoded letter.
@end table
Keys that lock/unlock a modifer should be suffixed
with a blank space and a @code{lock}. If the key is a
dead key (even the @key{Compose} key) should use
@code{dead} instead. A position, either @code{left},
@code{right}, @code{keypad} or an index, followed by
a blank space, should prefix any key that occurs on
multiple position on the keyboard, unless it only
appears on the keypad once and once not on the
keypad. Keys without any meaning should be identified
as @code{unknown}. Modifiers and dead keys should not
affect the value.

@item Optional header: @code{Characters}
UTF-8 encoded string that has been written.

@item Purpose:
Enable the user to use a keyboard, physical or
on-screen.

@item Purpose:
Enable programs to send keys as part of a script or a
reply of a recorded session.

@item Compulsivity:
Highly-recommended, a computer is as good as useless
without a keyboard.

@item Reference implementation:
@command{mds-kkbd}, @command{mds-kbd} and
@command{mds-keytrans}
@end table



@node enumerate-keyboards
@subsection @code{enumerate-keyboards}
@prindex @code{enumerate-keyboards}

@table @asis
@item Identifying header:
@code{Command: enumerate-keyboards}

@item Action:
List available keyboards.

@item Required header: @code{Client ID}
Your ID, provided by the @code{ID assignment}-header in
response to a @code{Command: assign-id}-header.

@item Instructions:
This message must be consumed by the first server that
receives it and implements support for it, and then
send out a @code{Command: keyboard-enumeration}
populated with the keyboard it provide as named in
the @code{Keyboard}-header for protocols such as
@code{Command: key-sent}.

@item Purpose:
Make it possible for clients to list all available
keyboards so that can be configured individually.

@item Compulsivity:
Optional.

@item Reference implementation:
@command{mds-kkbd} and @command{mds-kbd}
@end table



@node keyboard-enumeration
@subsection @code{keyboard-enumeration}
@prindex @code{keyboard-enumeration}

@table @asis
@item Identifying header:
@code{Command: keyboard-enumeration}

@item Action:
Response to @code{Command: enumerate-keyboards}.

@item Required header: @code{To}
The ID received under @code{Client ID}-header in the
@code{Command: enumerate-keyboards}-message that
triggered this message to be broadcasted

@item Required header: @code{In response to}
The ID received under the @code{Message ID}-header in
the @code{Command: enumerate-keyboards}-message that
triggered this message to be broadcasted.

@item Required header: @code{Length}
Length of the message.

@item Message:
New line separated list of available keyboards.

@item Instructions:
All keyboard servers should listen for this message
and append all keyboards it implement to the message
once recieved.

@item Purpose:
Make it possible for clients to list all available
keyboards so that can be configured individually

@item Compulsivity:
Required if you implement
@code{Command: enumerate-keyboards}.

@item Reference implementation:
@command{mds-kkbd} and @command{mds-kbd}
@end table



@node set-keyboard-leds
@subsection @code{set-keyboard-leds}
@prindex @code{set-keyboard-leds}

@table @asis
@item Identifying header:
@code{Command: set-keyboard-leds}

@item Action:
Activate and deactivate LED:s on a keyboard.

@item Required header: @code{Active}
LED:s that should be turned on. If a LED is listed
here but not in @code{Mask} that LED should be turned
on if it is off, and turned off if it is on.

The value is a single blank space separated list of
LED:s:
@table @code
@item num
@key{Num lock}
@item caps
@key{Caps lock}
@item scroll
@key{Scroll lock}
@item compose
@key{Compose}
@end table
Unsupported LED:s should be silently ignored.

@item Required header: @code{Mask}
LED:s listed here that do not appear in @code{Active}
should be turned off. The value of this header follows
the same rules as for @code{Active}.

@item Optional header: @code{Keyboard}
A string that identifies the keyboard that should be
affected. If omitted all keyboard are affected.

@item Purpose:
Enable keyboard layout servers to activate and
deactive LED:s on the keyboard to indicate active
locks.

@item Compulsivity:
Optional.

@item Reference implementation:
@command{mds-kkbd}, @command{mds-kbd} and
@command{mds-keytrans}
@end table



@node get-keyboard-leds
@subsection @code{get-keyboard-leds}
@prindex @code{get-keyboard-leds}

@table @asis
@item Identifying header:
@code{Command: get-keyboard-leds}

@item Action:
List exisiting LED:s on a keyboard and their state.

@item Required header: @code{Client ID}
Your ID, provided by the @code{ID assignment}-header in
response to a @code{Command: assign-id}-header.

@item Required header: @code{Keyboard}
A string that identifies the keyboard that should be
affected.

@item Response:
The server implementing support for
@code{Command: get-keyboard-leds} for the keyboard
indicated by @code{Keyboard} should send a message back
to the client indicated by the @code{Client ID}-header
(using the @code{To}-header) with the headers:
@table @code
@item Active
List of currently turned on LED:s.
@item Present
List of LED:s that the server believes to be present
on the keyboards.
@end table
Both of these headers followes the rules of the
@code{Active}-header under
@code{Command: set-keyboard-leds}.

@item Purpose:
Enable keyboard layout servers to automatically set
active locks when the server starts based on
currently active LED:s

@item Compulsivity:
Recommended. Required if you implement support for
@code{Command: set-keyboard-leds}. If you do not
support this protocol servers and clients and stall
when they try to get the active LED:s

@item Reference implementation:
@command{mds-kkbd}, @command{mds-kbd} and
@command{mds-keytrans}
@end table



@node set-keyboard-rate
@subsection @code{set-keyboard-rate}
@prindex @code{set-keyboard-rate}

@table @asis
@item Identifying header:
@code{Command: set-keyboard-rate}

@item Action:
Set the repeat rate and repeat delay on a keyboard.

@item Optional header: @code{Rate}
A floating point value of the repeat rate, measured
in cycles per second (hertz). Zero means no repeat.

@item Optional header: @code{Delay}
An unsigned 16-bit integer of the number of
milliseconds to wait before the first time a key is
repeated. Zero means that the delay is matched with
the rate, that is the reciprocal of the rate.

@item Optional header: @code{Emulate}
@table @code
@item disallow
Always use the keyboard's built in repeat feature.
@item allow
Use the keyboard's built in repeat feature when
possible, otherwise emulate the feature. But if the
selected settings are close enough to what the
keyboard supports, use the closed settings the
keyboard supports.
@item if needed
Use the keyboard's built in repeat feature when
possible, otherwise emulate the feature.
@item force
Never use the keyboard's built in repeat feature,
always emulate the feature.
@end table

@item Optional header: @code{Keyboard}
A string that identifies the keyboard that should be
affected. If omitted all keyboard are affected.

@item Instructions:
If neither of @code{Rate}, @code{Delay} and
@code{Emulate} headers are used. The server should
reapply the settings.

@item Purpose:
Enable the user to configure the repeat rate and
repeat delay on keyboards.

@item Compulsivity:
Optional.

@item Reference implementation:
@command{mds-kkbd} and @command{mds-kbd}
@end table



@node get-keyboard-rate
@subsection @code{get-keyboard-rate}
@prindex @code{get-keyboard-rate}

@table @asis
@item Identifying header:
@code{Command: get-keyboard-rate}

@item Action:
Get the repeat rate and repeat delay on a keyboard.

@item Required header: @code{Client ID}
Your ID, provided by the @code{ID assignment}-header in
response to a @code{Command: assign-id}-header.

@item Required header: @code{Keyboard}
A string that identifies the keyboard that should be
affected.

@item Response:
The server implementing support for
@code{Command: get-keyboard-rate} for the keyboard
indicated by @code{Keyboard} should send a message back
to the client indicated by the @code{Client ID}-header
(using the @code{To}-header) with the headers:
@table @code
@item Rate
The current repeat rate. Same syntax as in
@code{Command: set-keyboard-rate}. Set to
@code{unknown} if the server does not know what the
value is.
@item Delay
The current repeat delay. Same syntax as in
@code{Command: set-keyboard-rate}. Set to
@code{unknown} if the server does not know what the
value is.
@item Emulated
@table @code
@item yes
The server implements the key repeat in software.
@item no
The server has set the rate on the keyboard, and lets
the keyboard be responsible for the repeat. This
value should also be used if the server does not
support @code{Command: set-keyboard-rate} for the
enquired keyboard, but is the server that should be
responsible for it.
@end table
@end table

@item Purpose:
Enable the user to get the current repeat rate and
repeat delay on the keyboard.

@item Compulsivity:
Optional. Recommended if implement support for
@code{Command: set-keyboard-rate}. If you do not
support this protocol servers and clients and stall
when they try to get the current repeat rate and
repeat delay on the keyboard.

@item Reference implementation:
@command{mds-kkbd} and @command{mds-kbd}
@end table



@node keycode-map
@subsection @code{keycode-map}
@prindex @code{keycode-map}

@table @asis
@item Identifying header:
@code{Command: keycode-map}

@item Action:
Remap keyboard keycodes and query current mapping.

@item Required header: @code{Action}
@table @code
@item remap
Remap keys if the value of the header @code{Action}
is @code{remap}.
@item reset
Reset all mappings to identity mapping if the value
of the header @code{Action} is @code{reset}.
@item query
Query mapping if the value of the header @code{Action}
is @code{query}.
@end table
Each affected server will send a message format like
that of @code{Action: remap} with current mapping
that are not identity mappings.

@item Optional header: @code{Keyboard}
A string that identifies the keyboard that should be
affected. If omitted all keyboard are affected.

@item Conditionally required header: @code{Client ID}
Your ID, provided by the @code{ID assignment}-header in
response to a @code{Command: assign-id}-header.
Required if @code{Action: query} is included in the
headers.

@item Conditionally optional header: @code{Length}
The length of the message.
Available and optional if @code{Action: remap} is
included in the headers.

@item Message:
Each line contains contains two single space
delimited numbers, the first number is the keycode as
determined by the scancode, the second number is
keycode that scancode should generate. For example,
@code{1 1} resets @key{Escape} to be mapped to
@key{Escape}, and @code{1 59} remaps @key{Escape} to
@key{F1}, while
@example
@group
1 59
59 1
@end group
@end example
swaps @key{Escape} and @key{F1}.

@item Purpose:
Enable the user to swap or replace keys on the
keyboard.

@item Purpose:
Enable the user manually correct an incorrectly
mapped keyboard.

@item Compulsivity:
Optional.

@item Reference implementation:
@command{mds-kbd} and @command{mds-kkbd}
@end table



@node new-keyboard
@subsection @code{new-keyboard}
@prindex @code{new-keyboard}

@table @asis
@item Identifying header:
@code{Command: new-keyboard}

@item Action:
Announce the existance of a new keyboard.

@item Required header: @code{Length}
The length of the message.

@item Message:
List of strings that identifies the keyboards that
have been added.

@item Purpose:
Enable servers and clients to detect new keyboards.

@item Compulsivity:
Recommended.

@item Reference implementation:
@command{mds-kbd} and @command{mds-kkbd}
@end table



@node old-keyboard
@subsection @code{old-keyboard}
@prindex @code{old-keyboard}

@table @asis
@item Identifying header:
@code{Command: old-keyboard}

@item Action:
Announce the removal of an old keyboard.

@item Required header: @command{Length}
The length of the message.

@item Message:
List of strings that identifies the keyboards that
have been removed.

@item Purpose:
Enable servers and clients to detect removal of
keyboards.

@item Compulsivity:
Recommended.

@item Reference implementation:
@command{mds-kbd}
@end table



@node Clipboard Protocols
@section Clipboard Protocols

@menu
* clipboard::                       Read or manipulate a clipboard.
* clipboard-info::                  Clipboard event announcements.
@end menu



@node clipboard
@subsection @code{clipboard}
@prindex @code{clipboard}

@table @asis
@item Identifying header:
@code{Command: clipboard}

@item Action:
Read or manipulate a clipboard.

@item Required header: @code{Level}
The clipboard level, an [1, 3] integer:
@table @code
@item 1
Text copied/pasted using the keyboard or a menu item.
(This level is called `primary'.)
@item 2
Text copied/pasted using the rat.
(This level is called `secondary'.)
@item 3
Data to begin with a line describing the data type.
(This level is called `tertiary'.)
@end table

@item Required header: @code{Action}
What to do with the clipboard:
@table @code
@item add
Write the message to the clipboard if the value of
the header @code{Action} is @code{add}.
@item read
Read the clipboard if the value of the header
@code{Action} is @code{read}.
@item clear
Clear all entries on the selected level on the
clipboard if the value of the header @code{Action} is
@code{read}.
@item set-size
Shrink/grow the clipstack if the value of the header
@code{Action} is @code{set-size}.
@item get-size
Read the size of the clipstack if the value of the
header @code{Action} is @code{get-size}. In the
reply, the server will send a message containing the
headers:
@table @code
@item Size
The configured maximum size of the clipstack.
@item Used
The number of elements currently in the clipstack.
@end table
@end table

@item Conditionally required header: @code{Length}
Length of the message.
Required if @code{Action: add} is included in the
headers.

@item Conditionally required header: @code{Size}
The maximum number of elements in the clipstack.
Required if @code{Action: set-size} is included in
the headers.

@item Conditionally required header: @code{Client ID}
Your ID, provided by the @code{ID assignment}-header in
response to a @code{Command: assign-id}-header.
Required if @code{Action: read} or @code{Action: read}
is included in the headers, or if @code{Action: add}
is included in the headers and if the header
@code{Time to live} is included and has a value
starting with @code{until-death}.

@item Conditionally optional header: @code{Index}
The index of the item in the clipstack, starting at 0.
Available and optional if the @code{Action: read} is
included in the headers.

@item Conditionally optional header: @code{Time to live}
The number of seconds the entry should be available
before it is removed by the server, or:
@table @code
@item until-death
Remove entry when the client closes.
@item until-death #
Remove entry when the client closes, or @code{#}
seconds have elapsed.
@item forever
Never remove it. (This is the default.)
@end table
The server will always remove the entry when either:
@enumerate 1
@item
it is at the bottom of the clipstack and a new entry
is added to the clipstack, or
@item
@code{Action: clear} is issued for the clipstack.
@end enumerate
The entry will also be removed, unless
@code{Time to live: forever} is used, if the server
crashes or is re-executed.

@sgindex @code{SIGALRM}
It is up to the implementation to choose when the
removal actually takes place. For example, the
reference implementation will pop entries that have
timed out when a new entry is added, the reading on
the clipstack is requested or the server is
reexecuted, but another implement may choose to pop
entires asynchronously using another thread or an
alarm an pop when @code{SIGALRM} is received.

Available and optional if the @code{Action: add} is
included in the headers.

@item Message:
The content to add to the clipboard.

@item Purpose:
Enable the user to duplicate content from one process
into another process without requiring those processes
to be aware of eathother to any extent.

@item Compulsivity:
Optional.

@item Reference implementation:
@command{mds-clipboard}
@end table



@node clipboard-info
@subsection @code{clipboard-info}
@prindex @code{clipboard-info}

@table @asis
@item Identifying header:
@code{Command: clipboard-info}

@item Action:
The clipboard server sends out some information about
what it is doing, such as automatically removing
entires.

@item Included header: @code{Event}
@table @code
@item pop
The value of the header @code{Event} is @code{pop}
when an item in the clipstack has been removed. If
the value header--value-pair is used the following
headers will also be included in the message:
@table @code
@item Level
The clipboard level that has been affected.
@item Popped
The index of the item in the clipstack that has been
removed.
@item Size
The configured maximum size of the clipstack.
@item Used
The number of elements currently in the clipstack.
@end table
@item crash
The value of the header @code{Event} is @code{crash}
when the clipboard has been reset because of a
software crash.
@end table

@item Purpose:
Enable clients to get notification about changes to
the clipboard, that cannot trivially derived from
@code{Command: clipboard}

@item Compulsivity:
Optional add-on to the clipboard's functionallity.

@item Reference implementation:
@command{mds-clipboard}
@end table



@node Status Icon Protocols
@section Status Icon Protocols

@menu
* add-tray-icon::                   Add a status icons to the status icon tray.
* update-tray-icon::                Change the status of a status icon.
* tray-update::                     Send updates about the status tray to the status icon.
* new-tray::                        Announce the existence of a new status icon trays.
@end menu



@node add-tray-icon
@subsection @code{add-tray-icon}
@prindex @code{add-tray-icon}

@table @asis
@item Identifying header:
@code{Command: add-tray-icon}

@item Action:
Add a status icons to the status icon tray.

The client should keep in mind that there can be any
number of trays available on the system: zero, one,
two or three, …, and that it will get a response once
from every tray.

@item Required header: @code{Client ID}
Your ID, provided by the @code{ID assignment}-header in
response to a @code{Command: assign-id}-header.

@item Required header: @code{Package}
The name of the package to which the program
announced the icon belongs.

@item Required header: @code{Icon ID}
An ID of the icon that can be used identify the icon,
icon ID:s are not unique, but the combination of a
package and a icon ID should be unque and can be used
to ignore already added icons and hide icons that the
user has been configured to be hidden.

@item Required header: @code{Title}
A title describing the icon for the user, used to
configured when icons should be hidden and shown
among other configuration.

@item Required header: @code{Icon}
The name or pathname of an icon to use together with
the title.

@item Response:
Recipients will respond with a message containing the
headers:
@table @code
@item To
Will contain the value of the @code{Client ID} from
the message that triggered this response.
@item In response to
Will contain the value of the @code{Message ID} from
the message that triggered this response.
@item Message ID
Will contain a value as described in
@ref{Message Passing}.
@item Socket
Will contain an ID to where the icon should be
embeded.
@item Will send update
The value of this header will be @code{yes} if this
message will be followed by a
@code{Command: tray-update}-message. Otherwise the
value will be @code{no}.
@end table

@item Purpose:
Enable clients to add a small icon that displays the
status of programs, particularly minimised programs
and services.

@item Compulsivity:
Optional.
@end table



@node update-tray-icon
@subsection @code{update-tray-icon}
@prindex @code{update-tray-icon}

@table @asis
@item Identifying header:
@code{Command: update-tray-icon}

@item Action:
Change the status of a status icon.

@item Required header: @code{Status}
@table @code
@item hide
Hide the icon if the value of the
@code{Status}-header is @code{hide}.
@item show
Show the icon if the value of the
@code{Status}-header is @code{show}.
@item active
The icon is active if the value of the
@code{Status}-header is @code{active}.
@item inactive
The icon is inactive if the value of the
@code{Status}-header is @code{inactive}.
@end table

@item Purpose:
Enable status trays to automatically hide inactive
icons.

@item Purpose:
Hide icons without actually removing them.

@item Compulsivity:
Required if supporting @code{Command: add-tray-icon},
only @code{Status: hide} and @code{Status show} is
required.
@end table



@node tray-update
@subsection @code{tray-update}
@prindex @code{tray-update}

@table @asis
@item Identifying header:
@code{Command: tray-update}

@item Action:
Send updates about the status tray to the status icon.

@item Required header: @code{Socket}
Where the icon is embedded, used to identify the
affected tray.

@item Conditionally required header: @code{Max colour}
The maximum colour component value, for example, if
using 24-bit colour, which component will be 8-bit
and the maximum value will be 255, this also applies
to the alpha component. Required if either for the
@code{Colour}-, @code{Foreground}- or
@code{Alpha}-header are used.

@item Conditionally required header: @code{Size}
The width and height, in pixels, the icon should have.
Required if the @code{Length}-header is used,
otherwise this header is optional.

@item Conditionally required header: @code{Has alpha}
@table @code
@item yes
The message contains an alpha channel if the value of
the @code{Has alpha} header is @code{yes}.
@item no
The message does not contain an alpha channel if the
value of the @code{Has alpha}-header is @code{no}.
@end table
Required if the @code{Length}-header is used.

@item Conditionally required header: @code{Bytes}
The number of bytes the subpixels used, for example,
24-bit colours will have this set to 1 because each
subpixel has 8 bits, 48-bit colours will have this
set to 2 because each subpixel has 16 bits. Allowed
values are: 1, 2, 4 and 8. These values are used so
that CPU:s with any endianness can be trivially used
as the words sizes are guaranteed to be supported in
C, and mixed/middle-endiannes gets complicated if we
go outside this. Required if the @code{Length}-header
is used.

@item Conditionally optional/required header: @code{Colour}
Single blank space-separated [0, @code{<Max colour>}]
sRGB 3-tuple.
Available and optional if the @code{Length}-header
is not used.
Required if the @code{Foreground}-header but not
@code{Length}-header is used.

@item Conditionally optional header: @code{Foreground}
Single blank space-separated [0, @code{<Max colour>}]
sRGB 3-tuple.

@item Optional header: @code{Alpha}
The opacity of the tray.

@item Optional header: @code{Length}
Length of the message.

@item Optional header: @code{Use urgency}
@table @code
@item yes
The icon tray may blink if the value of the
@code{Use urgency}-header is @code{yes}.
@item no
The icon tray may not blink if the value of the
@code{Use urgency}-header is @code{no}.
@end table

@item Message:
Raw binary encoding of the background image, bytes
are orders: row, pixel, channel (alpha, red, green,
blue), subpixel value (native CPU encoding). The
Alpha channel should be included but ignored if
@code{Has alpha: no}, in such as it is best to set it
to full.

@ifset AFOURPAPER_OR_USLETTER
Example image with @code{Bytes: 2},
@code{Has alpha: no} and @code{Size: 3}:
@example
@group
sRGB(x0102, 0, 0), sRGB(0, x0304, 0), sRGB(0, 0, x0506)
sRGB(x0708, 0, 0), sRGB(0, x090A, 0), sRGB(0, 0, x0B0C)
sRGB(x0D0E, 0, 0), sRGB(0, x0F10, 0), sRGB(0, 0, x1112)
@end group
@end example

Encoding of example image in hexadecimal
representation:
@example
@group
FFFF 0102 0000 0000 FFFF 0000 0304 0000 FFFF 0000 0000 0506
FFFF 0708 0000 0000 FFFF 0000 090A 0000 FFFF 0000 0000 0B0C
FFFF 0D0E 0000 0000 FFFF 0000 0F10 0000 FFFF 0000 0000 1112
@end group
@end example

Note that on a big-endian system this would be:
@footnote{x86_64 computers are big-endian.}
@example
@group
FF FF 02 01 0 0 0 0 FF FF 0 0 04 03 0 0 FF FF 0 0 0 0 06 05
FF FF 08 07 0 0 0 0 FF FF 0 0 0A 09 0 0 FF FF 0 0 0 0 0C 0B
FF FF 0E 0D 0 0 0 0 FF FF 0 0 10 0F 0 0 FF FF 0 0 0 0 12 11
@end group
@end example
@end ifset
@ifclear AFOURPAPER_OR_USLETTER
Example image with @code{Bytes: 2},
@code{Has alpha: no} and @code{Size: 2}:
@example
@group
sRGB(x0102, 0, 0), sRGB(0, x0304, 0)
sRGB(x0708, 0, 0), sRGB(0, x090A, 0)
@end group
@end example

Encoding of example image in hexadecimal
representation:
@example
@group
FFFF 0102 0000 0000 FFFF 0000 0304 0000
FFFF 0708 0000 0000 FFFF 0000 090A 0000
@end group
@end example

Note that on a big-endian system this would be:
@footnote{x86_64 computers are big-endian.}
@example
@group
FF FF 02 01 0 0 0 0 FF FF 0 0 04 03 0 0
FF FF 08 07 0 0 0 0 FF FF 0 0 0A 09 0 0
@end group
@end example
@end ifclear

It is up to the networking servers to translate the
encoding between machines.@footnote{The host
translates to big-endian unless they can confirm that
they have the same endianness.}

@item Purpose:
Enable clients to be aware of the appearance of the
tray, such as colours, transparency and background
image.

@item Purpose:
Enable clients to be aware of how the user wants
status icons to behave.

@item Compulsivity:
Optional.
@end table



@node new-tray
@subsection @code{new-tray}
@prindex @code{new-tray}

@table @asis
@item Identifying header:
@code{Command: new-tray}

@item Action:
Announce the existence of a new status icon trays.

@item Purpose:
Allow clients to add their status icons to status icon
trays that have been added to the display after those
programs have started and attempted to add their
icons.

@item Compulsivity:
Required if supporting @code{Command: add-tray-icon}.
@end table



@node Colour Protocols
@section Colour Protocols

@menu
* get-gamma-info::                  Query gamma ramp information.
* get-gamma::                       Query gamma ramps.
* set-gamma::                       Modify gamma ramps.
@end menu



@node get-gamma-info
@subsection @code{get-gamma-info}
@prindex @code{get-gamma-icon}

@table @asis
@item Identifying header:
@code{Command: get-gamma-info}

@item Action:
Query gamma ramp information.

@item Required header: @code{Client ID}
Your ID, provided by the @code{ID assignment}-header in
response to a @code{Command: assign-id}-header.

@item Required header: @code{CRTC}
The output name for the CRTC of interest.

@item Response:
The server will response with a @code{Command: error}
on error, unsuccess the server will respond with a
message contain the headers:
@table @code
@item To
Will contain the value of the header @code{Client ID}
in the message that was received by the server.
@item In response to
Will contain the value of the header @code{Message ID}
in the message that was received by the server.
@item Cooperative
Whether a server like @command{mds-coopgamma} is
running. That is, if priorities and classes are
respected. The value with be either @code{yes}, for
cooperative, or @code{no}, for non-cooperative.
@item Depth
The bit-depth of the gamma ramps. Possible values
are: 8, 16, 32 och 64.
@item Red size
The number of stops in the red gamma ramp.
@item Green size
The number of stops in the green gamma ramp.
@item Blue size
The number of stops in the blue gamma ramp.
@item Gamma support
Will have one of the following values:
@table @code
@item yes
It is known that gamma ramps are supported.
@item no
It is known that gamma ramps are not supported.
@item maybe
It is now known whether gamma ramps are supported.
@end table
@end table
If @code{Gamma support: no} is send in the response,
the headers @code{Depth}, @code{Red size},
@code{Green size} and @code{Blue size} may be omitted.

@item Purpose:
Enable performance optimisation when manipulating
gamma ramps.

@item Compulsivity:
Optional. Required if your implement support for
@code{Command: get-gamma} or @code{Command: set-gamma}.

@item Reference implementation:
@command{mds-hwgamma}, @command{mds-swgamma},
@command{mds-coopgamma} and @command{mds-cursorgamma}.
@end table



@node get-gamma
@subsection @code{get-gamma}
@prindex @code{get-gamma}

@table @asis
@item Identifying header:
@code{Command: get-gamma}

@item Action:
Query gamma ramps.

@item Required header: @code{Client ID}
Your ID, provided by the @code{ID assignment}-header
in response to a @code{Command: assign-id}-header.

@item Required header: @code{CRTC}
The output name for the CRTC of interest.

@item Required header: @code{Coalesce}
Whether the received the full gamma ramp filter list,
of the value is @code{yes}, rather than the result of
them, of the value is @code{no}.

@item Required header: @code{High priority}
The upper bound of the priority range of the gamma
ramps to received. This is a signed 64-bit integer.

@item Required header: @code{Low priority}
The lower bound of the priority range of the gamma
ramps to received. This is a signed 64-bit integer.

@item Response:
The server will response with a @code{Command: error}
on error, unsuccess the server will respond with a
message contain the headers:
@table @code
@item Depth
The bit-depth of the gamma ramps. Possible values
are: 8, 16, 32 och 64.
@item Red size
The number of stops in the red gamma ramp.
@item Green size
The number of stops in the green gamma ramp.
@item Blue size
The number of stops in the blue gamma ramp.
@item Tables
The number of gamma ramp lookup tables that is
included in the respone's message. This header will
not necessarily be included if @code{Coalesce: yes}
was used in the query, rather reference
implementations will exclude it.
@end table
These headers are included so you can make sure the
no metadata for gamma ramps have changed, which could
happen if the user switches between hardware and
software gamma ramps. The response will also contain
a @code{Length}-header and a message formatted in the
same manner as for @code{Command. set-gamma}-messages.
That is, assuming as an example that the gamma ramp
depth is 16 bits, @code{Coalesce: yes} was used in the
query, the red ramp is (1, 2, 3, 4, 5, 6), the green
ramp is (17, 18, 19, 20, 21, 22, 23) and the blue ramp
is (33, 34, 35, 36, 37, 38, 39, 40) then the message
will be (hexadecimal representation):
@example
@group
0001 0002 0003 0004 0005 0006
0011 0012 0013 0014 0015 0016 0017
0021 0022 0023 0024 0025 0026 0027 0028
@end group
@end example

On a big-endian system this would be:
@example
@group
01 00 02 00 03 00 04 00 05 00 06 00
11 00 12 00 13 00 14 00 15 00 16 00 17 00
21 00 22 00 23 00 24 00 25 00 26 00 27 00 28 00
@end group
@end example

However if @code{Coalesce: no} was used in the query,
the message will include multiple gamma ramps lookup
tables. These will be in the order they are applied,
that is, highest priority first. The tables will be
encoded in the same way as for @code{Coalesce: yes}
and they with be included without any delimiter.
However, each table will be prefixed with the priority
and the class. The priority will be encoded in native
binary format as an @code{int64_t} and the class will
be encoded as a NUL-terminated UTF-8 string

@item Purpose:
Enable analysis and readings of the current gamma
ramps.

@item Compulsivity:
Optional. Required if your implement support for
@code{Command: get-gamma-info} or
@code{Command: set-gamma}.

@item Reference implementation:
@command{mds-hwgamma}, @command{mds-swgamma},
@command{mds-coopgamma} and @command{mds-cursorgamma}.
@end table



@node set-gamma
@subsection @code{set-gamma}
@prindex @code{set-gamma}

@table @asis
@item Identifying header:
@code{Command: set-gamma}

@item Action:
Modify gamma ramps.

@item Required header: @code{Client ID}
Your ID, provided by the @code{ID assignment}-header
in response to a @code{Command: assign-id}-header.

@item Required header: @code{CRTC}
The output name for the CRTC of interest.

@item Required header: @code{Priority}
A signed 64-bit integer of the priority for the
filter. gamma correction should use zero priority. It
is preferable that search logical adjustment is sent
with different priorities so other programs can
insert filters between them.

@item Required header: @code{Class}
A UTF-8 string that identifies the filter. It should
be formatted as @code{pkg::cmd::role}. @code{pkg}
should be the package name the package was installed
with on the system. @code{cmd} should be the basename
of the command for the program.

@item Required header: @code{Lifespan}
The value may be one of the following:
@table @code
@item until-removal
Remove the filter when @command{Lifespan: remove} is
sent.
@item until-death
Remove the filter when the client dies.
@item remove
Remove the filter now.
@end table

@item Conditionally required header: @code{Length}
The length of the message.
Available and required if @code{Lifespan: remove} is
not included in the message.

@item Message:
The gamma ramps in binary encoding. As an example,
assume the gamma ramp depth is 16 bits, the red ramp
is (1, 2, 3, 4, 5, 6), the green ramp is (17, 18, 19,
20, 21, 22, 23) and the blue ramp is (33, 34, 35, 36,
37, 38, 39, 40) then the message will be (hexadecimal
representation):
@example
@group
0001 0002 0003 0004 0005 0006
0011 0012 0013 0014 0015 0016 0017
0021 0022 0023 0024 0025 0026 0027 0028
@end group
@end example

Note that on a big-endian system this would be:
@footnote{x86_64 computers are big-endian.}
@example
@group
01 00 02 00 03 00 04 00 05 00 06 00
11 00 12 00 13 00 14 00 15 00 16 00 17 00
21 00 22 00 23 00 24 00 25 00 26 00 27 00 28 00
@end group
@end example

It is up to the networking servers to translate the
encoding between machines.@footnote{The host
translates to big-endian unless they can confirm that
they have the same endianness.}

The use of binary rather than text here is chosen to
increase performance for programs that try the change
the adjustments fluently. For programs similar to
@command{xgamma} that sets the ramps once this is
however unnessary. However it does simplify the
program code as one would only need to write the
ramps to the message without creating a string with
all stops converted and then measure the length of
that string.

@item Response:
The server will response with a @code{Command: error}.

@item Instructions:
For optimal flexibility a system may run a server such
as @command{mds-hwgamma} that applies the gamma ramps,
and a server such as @command{mds-coopgamma} to let
multiple programs adjust the output with their open
filters that stack up. In a configuration like this,
@command{mds-coopgamma} will keep track of all filters
and when a modification is made it sends the grand
result to @command{mds-hwgamma}, that is, what the
filters together produce. To do this,
@command{mds-coopgamma} listens for
@code{Command: set-gamma} with priority @math{2^{62}}
and modifies the message so the payload is filled with
the result rather than to single filter. This modified
message is then received by @command{mds-hwgamma} that
listens with priority zero and applies the gamma ramps.
@command{mds-hwgamma} will ignore the @code{Priority}
and the @code{Class}-header, but it will respect the
@code{Lifespan}-header, therefore
@command{mds-coopgamma} will always modify the value
of the @code{Lifespan}-header to @code{until-removal}.

@item Purpose:
Enable colour output correction such as gamma
correction.

@item Purpose:
Enable colour output filters such colour temperature
adjustments, colour invertion and dimming.

@item Compulsivity:
Optional. Required if your implement support for
@code{Command: get-gamma-info} or
@code{Command: get-gamma}.

@item Reference implementation:
@command{mds-hwgamma}, @command{mds-swgamma},
@command{mds-coopgamma} and @command{mds-cursorgamma}.
@end table



@node Screensaver Protocols
@section Screensaver Protocols

@menu
* configure-screensaver::           Configure screensaver settings.
* start-screensaver::               Start the screensaver.
* screensaver-start-test::          Test whether the screensaver may start.
@end menu



@node configure-screensaver
@subsection @code{configure-screensaver}
@prindex @code{configure-screensaver}

@table @asis
@item Identifying header:
@code{Command: configure-screensaver}

@item Action:
Reconfigure screensaver settings, or tell the
screensaver server that the screensaver may not start
whilst a program is active.

@item Optional header: @code{Screensaver}
The command, in POSIX shell syntax, for the command
to run to start the screensaver. The screensaver
server will be inactive as long as the spawn command
has not exited. To disable screensaving, the value
for this header should be @command{true}. This
command always starts without fail, and does nothing.
Which means that the a screensaver will not start,
and the panic action cannot start is it would if the
values as set to @command{false}. The screensaver
server may choose recognise the command
@command{true} as meaning that does not need to start
a screensaver. It is also possible to disable
screensaving via the @code{Activate delay}-header.

@item Optional header: @code{Activate delay}
The number of seconds the display should be inactive
before the screensaver should start. Floating points
are allowed. The value @code{0} is discouraged, but
has the same meaning as @code{disable}, which means
that the screensaver should never start.

@item Optional header: @code{Lock delay}
The number of seconds to wait after the screensaver
starts before authentication via login passphrase is
required to deactivate the screensaver. Floating
points are allowed. If properly formatted, the
environment variable @env{MDS_SCREENSAVER_LOCK} is
set to have this value. If the value is
@code{disable}, the environment variable
@env{MDS_SCREENSAVER_LOCK} will be cleared, which
should be interpreted by the screensaver as that it
should not start the lock mechanism.

@item Optional header: @code{Panic on error}
The command, in POSIX shell syntax, to run if the
screensaver exits without another value than 0. If
you do no want anything to happen, choose either of
the values @command{true} or @command{false}. This is
intended as a security measure, in case the
screensaver fails to start the lock mechanism.

@item Optional header: @code{DPMS}
TODO

@item Optional header: @code{Inhibit}
@table @code
@item yes
The screensaver may not start whilst the client is
connected to the server.
@item no
Undo the action set by @code{Inhibit: yes} and the
same client.
@end table

@item Conditionally required header: @code{Client ID}
Your ID, provided by the @code{ID assignment}-header
in response to a @code{Command: assign-id}-header.
Required if @code{Inhibit} is included in the headers.

@item Purpose:
Allow the user to change screensaver settings.

@item Purpose:
Allow programs to stop the screensaver from starting.

@item Compulsivity:
Optional.

@item Reference implementation:
@command{mds-screensaver}
@end table



@node start-screensaver
@subsection @code{start-screensaver}
@prindex @code{start-screensaver}

@table @asis
@item Identifying header:
@code{Command: start-screensaver}

@item Action:
Start the screensaver, either timed or forced.

@item Instructions:
The screensaver server should broadcast this command
when the display has been active for long enough for
the screensaver to start. It should then intercept
the message, including messages with this command
that is not send from the screensaver server itself,
with priority @math{-2^{63}}. The screensaver should
be started when this message is intercepted by the
screensaver server. All servers that need to perform
actions before the switch takes place must have a
priority higher than @math{-2^{63}}, preferably 0.
Server that can perform their actions asynchronously
should intercept the message without modifying
capabilities.

@item Purpose:
Allow users to force the screensaver to start.

@item Purpose:
Allow the screensaver daemon to notify servers when
the screensaver starts.

@item Compulsivity:
Optional.

@item Reference implementation:
@command{mds-screensaver}
@end table



@node screensaver-start-test
@subsection @code{screensaver-start-test}
@prindex @code{screensaver-start-test}

@table @asis
@item Identifying header:
@code{Command: screensaver-start-test}

@item Action:
Ask servers when they last were active.

@item Required header: @code{Last active}
The message broadcaster should set the value of this
header to 0. Any server intercepting this message
should set value to the last time (monotonic time,
preferably raw) the server observed actions that
means that the display is active, such as usage of
the keyboard or rat. The servers should however not
modify the value if the value they would set it to
is lower than the already set value. Floating points
are allowed.

@item Instructions:
The screensaver server should broadcast this message
when it thinks it can start the screensaver. It
should intercept this message with priority
@math{-2^{63}}. When intercepted it should read the
@code{Last active}-header to determine the next time
the screensaver is allowed to start, which means that
it should add the activate delay to this value. If
the calculate time is in the past, the screensaver
server should broadcast the
@command{start-screensaver}-message to start the
screensaver.

@item Purpose:
Allow the screensaver to as servers like the input
device servers whether it is the for the screensaver
to start, instead of needing to listening on all
input devices.

@item Compulsivity:
Optional.

@item Reference implementation:
@command{mds-screensaver}, @command{mds-kkbd},
@command{mds-kbd} and @command{mds-rat}
@end table



@node Miscellaneous Protocols
@section Miscellaneous Protocols

@menu
* echo::                            Echo back a message.
* kill::                            The window killing protocol.
@end menu



@node echo
@subsection @code{echo}
@prindex @code{echo}

@table @asis
@item Identifying header:
@code{Command: echo}

@item Action:
Echo back a message.

@item Required header: @code{Client ID}
Your ID, provided by the @code{ID assignment}-header
in response to a @code{Command: assign-id}-header.

@item Optional header: @code{Length}
Length of the message.

@item Message:
Message to echo.

@item Purpose:
Debugging and testing.

@item Purpose:
Network heartbeat.

@item Compulsivity:
Recommended for network enabled servers.

@item Reference implementation:
@command{mds-echo}
@end table



@node kill
@subsection @code{kill}
@prindex @code{kill}

@table @asis
@item Identifying header:
@code{Command: kill}

@item Action:
Kill and identify processes based on the their
windows.

@item Required header: @code{Client ID}
Your ID, provided by the @code{ID assignment}-header
in response to a @code{Command: assign-id}-header.

@item Required header: @code{Window ID}
The ID of the window whose owning process should
be identified or signaled.

@item Required header: @code{Signal}
A numerical value of the signal to send to the
process. It is up to networking protocols to
translate these numbers of the display spans
multiple operating systems. The signal zero can
usually be used if no signal is to be sent, this is
however dependent on the operating system.

@item Response:
The server will respond with a
@code{Command: error}-message. In this message the
server all include an ad-hoc header:
@code{Process ID}@. Its value will be the ID of the
process that owns the window.

@item Purpose:
Identify and send signal to processes by refering to
them by one of their windows.

@item Compulsivity:
Optional.

@item Reference implementation:
@command{mds-kill} and @command{mds-slay}
@end table



@node libmdsserver
@chapter libmdsserver

libmdsserver is library written for the reference
implementation of the @command{mds} servers.
llibmdsserver does not contain support or any
protocols, rather it contains auxiliary functions,
macros, data structures such as linked lists and hash
tables, and support the basics of the message passing
protocol: receiving message and decode it into
headers and payloads.

@menu
* Macros::                          Writing macroscopic systems.
* Auxiliary Functions::             Auxiliary functions for servers.
* Data Structures::                 Data structures available in libmdsserver.
@end menu



@node Macros
@section Macros

The header file @file{<libmdsserver/macros.h>}
contains macros for readability and code reduction,
it also contains macros and definitions for
portability; they may either provide portability by
nature, or provide one place to do modifications to
port the system.

@table @asis
@item @code{xasprintf} [(@code{char* buffer, ...}) @arrow{} @code{int}]
@fnindex @code{xasprintf}
@cpindex Functions, printing
@cpindex Printing fuction
This is a wrapper for @code{asprintf} that has two
important properties, the buffer is guaranteed to be
@code{NULL} on failure, and it will return zero on
and only on success. Unlike @code{asprintf},
@code{xasprintf} takes the buffer's variable as its
first argument rather than the address of that
variable.

@item @code{xsnprintf} [(@code{char buffer[], ...}) @arrow{} @code{int}]
@fnindex @code{xsnprintf}
@cpindex Functions, printing
@cpindex Printing fuction
This is a wrapper for @code{snprintf} that allows you
to forget about the buffer size. When you know how
long a string can be, you should use @code{sprintf}.
But when you cannot know for sure you should use
@code{xsnprintf}. @code{xsnprintf} works exactly as
@code{sprintf}, but it will require that the first
argument is defined using @code{[]} rather than
@code{*} because it will use this to find out how
large the buffer is so it can call @code{snprintf}
with that size.

@item @code{eprint} [(@code{const char* format}) @arrow{} @code{int}]
@fnindex @code{eprint}
@cpindex Functions, printing, errors
@cpindex Printing fuction, errors
@cpindex Error printing function
A wrapper for @code{fprintf} that prints a string
prefixed with the value of @code{*argv} to
@code{stderr}. This wrapper also as a line feed to
the end of the text. Because @code{eprintf} naïvely
wraps @code{fprintf}, all `%':s in the string must be
duplicated.

@item @code{eprintf} [(@code{const char* format, ...}) @arrow{} @code{int}]
@fnindex @code{eprintf}
@cpindex Functions, printing, errors
@cpindex Printing fuction, errors
@cpindex Error printing function
@code{eprint} extends @code{eprint} with variadic
arguments that can be used to insert values into the
format string just like you can do in @code{fprintf}.

@item @code{iprint} [(@code{const char* format}) @arrow{} @code{int}]
@fnindex @code{iprint}
@cpindex Functions, printing, state
@cpindex Printing fuction, state
@cpindex State printing function
@sgindex @code{SIGINFO}
@cpindex State dump
@cpindex Statistics dump
A wrapper for @code{fprintf} that prints a string
prefixed with the value of @code{*argv}, as well a
label telling the user that the output is part of a
state and statistics dump, to @code{stderr}. This
wrapper also as a line feed to the end of the text.
Because @code{eprintf} naïvely wraps @code{fprintf},
all `%':s in the string must be duplicated.

@item @code{iprintf} [(@code{const char* format, ...}) @arrow{} @code{int}]
@fnindex @code{iprintf}
@cpindex Functions, printing, state
@cpindex Printing fuction, state
@cpindex State printing function
@sgindex @code{SIGINFO}
@cpindex State dump
@cpindex Statistics dump
@code{eprint} extends @code{iprint} with variadic
arguments that can be used to insert values into the
format string just like you can do in @code{fprintf}.

@item @code{with_mutex} [(@code{pthread_mutex_t mutex, instructions})]
@fnindex @code{with_mutex}
@cpindex Threading, synchronisation
@cpindex Multi-threading, synchronisation
@cpindex Synchronisation, threading
@cpindex Mutex
Wraps @code{instructions} with
@code{errno = pthread_mutex_lock(mutex);} and
@code{errno = pthread_mutex_unlock(mutex);}, so a set
of instructions can be invoked inside mutex
protection.

@item @code{with_mutex_if} [(@code{pthread_mutex_t mutex, condition, instructions})]
@fnindex @code{with_mutex_if}
@cpindex Threading, synchronisation
@cpindex Multi-threading, synchronisation
@cpindex Synchronisation, threading
@cpindex Mutex
An alternative to @code{with_mutex} where
@code{instructions} is wrapped around
@code{if (condition)} which in turn is wrapped inside
the mutex protection.

@item @code{max} [(@code{a, b})]
@fnindex @code{max}
@cpindex Value comparision macro
Returns the higher value of @code{a} and @code{b}.

@item @code{min} [(@code{a, b})]
@fnindex @code{min}
@cpindex Value comparision macro
Returns the lower value of @code{a} and @code{b}.

@item @code{buf_cast} [(@code{char* buffer, type, size_t index})]
@fnindex @code{buf_cast}
@cpindex Re-executing servers, macros
@cpindex Updating, online, macros
@cpindex Online updating, macros
@cpindex Version update, macros
@cpindex Serialisation macros
@cpindex Marshalling macros
@sgindex @code{SIGUPDATE}
Casts @code{buffer} to a @code{type} buffer and
subscripts to the @code{index}:th element. You can
either use this function as a getter or a setter.

@item @code{buf_set} [(@code{char* buffer, type, size_t index, type variable}) @arrow{} @code{type}]
@fnindex @code{buf_set}
@cpindex Re-executing servers, macros
@cpindex Updating, online, macros
@cpindex Online updating, macros
@cpindex Version update, macros
@cpindex Serialisation macros
@cpindex Marshalling macros
@sgindex @code{SIGUPDATE}
Wrapper for @code{buf_cast} that sets the addressed
element to the value of @code{variable}.

@item @code{buf_get} [(@code{const char* buffer, type, size_t index, type variable}) @arrow{} @code{type}]
@fnindex @code{buf_get}
@cpindex Re-executing servers, macros
@cpindex Updating, online, macros
@cpindex Online updating, macros
@cpindex Version update, macros
@cpindex Serialisation macros
@cpindex Marshalling macros
@sgindex @code{SIGUPDATE}
Wrapper for @code{buf_cast} that sets the value of
@code{variable} to the value of the addressed element.

@item @code{buf_next} [(@code{char* buffer, type, size_t count}) @arrow{} @code{char*}]
@fnindex @code{buf_next}
@cpindex Re-executing servers, macros
@cpindex Updating, online, macros
@cpindex Online updating, macros
@cpindex Version update, macros
@cpindex Serialisation macros
@cpindex Marshalling macros
@sgindex @code{SIGUPDATE}
Increases the pointer @code{buffer} by the size of
@code{type} @code{count} types.

@item @code{buf_prev} [(@code{char* buffer, type, size_t count}) @arrow{} @code{char*}]
@fnindex @code{buf_prev}
@cpindex Re-executing servers, macros
@cpindex Updating, online, macros
@cpindex Online updating, macros
@cpindex Version update, macros
@cpindex Serialisation macros
@cpindex Marshalling macros
@sgindex @code{SIGUPDATE}
Decreases the pointer @code{buffer} by the size of
@code{type} @code{count} types.

@item @code{buf_set_next} [(@code{char* buffer, type, type variable}) @arrow{} @code{type}]
@fnindex @code{buf_set_next}
@cpindex Re-executing servers, macros
@cpindex Updating, online, macros
@cpindex Online updating, macros
@cpindex Version update, macros
@cpindex Serialisation macros
@cpindex Marshalling macros
@sgindex @code{SIGUPDATE}
@example
@group
buf_set(buffer, type, 0, variable),
buf_next(buffer, type, 1);
@end group
@end example

@item @code{buf_get_next} [(@code{char* buffer, type, type variable}) @arrow{} @code{type}]
@fnindex @code{buf_get_next}
@cpindex Re-executing servers, macros
@cpindex Updating, online, macros
@cpindex Online updating, macros
@cpindex Version update, macros
@cpindex Serialisation macros
@cpindex Marshalling macros
@sgindex @code{SIGUPDATE}
@example
@group
buf_get(buffer, type, 0, variable),
buf_next(buffer, type, 1);
@end group
@end example

@item @code{strequals} [(@code{const char* a, const char* b}) @arrow{} @code{int}]
@fnindex @code{strequals}
@cpindex String comparison
Evaluates whether the strings @code{a} and @code{b}
are equals, neither may be @code{NULL}@.

@item @code{startswith} [(@code{const char* haystack, const char* needle}) @arrow{} @code{int}]
@fnindex @code{startswith}
@cpindex String comparison
Evaluates whether the string @code{haystack}
starts with the string @code{needle}, neither
may be @code{NULL}@.

@item @code{drop_privileges} [(void) @arrow{} @code{int}]
@fnindex @code{drop_privileges}
@cpindex Previleges
@cpindex Security, previleges
Sets the effective user to the real user and the
effective group to the real group. This is used by
most servers and ensure that they are not running
with unnecessary privileges. Returns zero on and only
on success.

@item @code{monotone} [(@code{struct timespec* time_slot}) @arrow{} @code{int}]
@fnindex @code{monotone}
@cpindex Time, monotonic
@cpindex Monotonic time
Stores the time of an unspecified monotonic clock
into @code{time_slot}. Returns zero on and only on
success.

@item @code{close_files} [(@code{condition}) @arrow{} @code{void}]
@fnindex @code{close_files}
@cpindex File descriptions, close all
@cpindex Close all file descriptions
Closes all file descriptors named by a variable
@code{fd} for which @code{condition} evalutes to
non-zero.

@item @code{xfree} [(@code{void** array, size_t elements}) @arrow{} @code{void}]
@fnindex @code{xfree}
@cpindex Memory management
Calls @code{free} on the first @code{elements}
elements in @code{array}, and than calls @code{free}
on @code{array}. This macro requires @code{size_t i}
is declared.

@item @code{xmalloc} [(@code{type* var, size_t elements, type}) @arrow{} @code{int}]
@fnindex @code{xmalloc}
@cpindex Memory management
Allocates a @code{type*} with @code{elements}
elements and stores the allocated pointer to
@code{var}. Returns zero on and only on success.

@item @code{xbmalloc} [(@code{type* var, size_t bytes}) @arrow{} @code{int}]
@fnindex @code{xbmalloc}
@cpindex Memory management
Allocates @code{bytes} bytes and stores the allocated
pointer to @code{var}. Returns zero on and only on
success.

@item @code{xcalloc} [(@code{type* var, size_t elements, type}) @arrow{} @code{int}]
@fnindex @code{xcalloc}
@cpindex Memory management
Allocates a zero-initialised @code{type*} with
@code{elements} elements and stores the allocated
pointer to @code{var}. Returns zero on and only on
success.

@item @code{xbcalloc} [(@code{type* var, size_t bytes}) @arrow{} @code{int}]
@fnindex @code{xbcalloc}
@cpindex Memory management
Allocates and zero-initialises @code{bytes} bytes and
stores the allocated pointer to @code{var}. Returns
zero on and only on success.

@item @code{xrealloc} [(@code{type* var, size_t elements, type}) @arrow{} @code{int}]
@fnindex @code{xrealloc}
@cpindex Memory management
Reallocates @code{var} and updates the variable
@code{var} accordingly. @code{var} will be allocated
to have @code{elements} elements of the type
@code{type}. If @code{var} is @code{NULL} a new
allocation is created. If @code{elements} is zero,
@code{var} will be deallocated. Returns zero on and
only on success. On failure, @code{var} will be
@code{NULL}, so you must store the @code{var} into
another variable in case this macro fails.

@item @code{xxrealloc} [(@code{type* old, type* var, size_t elements, type}) @arrow{} @code{int}]
@fnindex @code{xxrealloc}
@cpindex Memory management
Variant of @code{xrealloc} that will return with
@code{old} set to @code{NULL} on success, and
@code{old} set to @code{var} on error. Like
@code{xrealloc}, @code{xxrealloc} returns zero on and
only on success.

@item @code{yrealloc} [(@code{type* tmp, type* var, size_t elements, type}) @arrow{} @code{int}]
@fnindex @code{yrealloc}
@cpindex Memory management
Variant of @code{xrealloc} that will store @code{var}
to @code{tmp} before reallocating @code{var} and then
restore @code{var} if the reallocation failed. Like
@code{xrealloc}, @code{yrealloc} returns zero on and
only on success.

@item @code{growalloc} [(@code{type* old, type* var, size_t elements, type}) @arrow{} @code{int}]
@fnindex @code{growalloc}
@cpindex Memory management
When using this macro @code{var} should be a
@code{type*} pointer allocated for @code{elements}
elements of the type @code{type}. This macro will
reallocate @code{var} to contain twice as many
elements and update @code{elements} accordingly. On
failure nothing changes. You must specify a
 auxiliary @code{type*} variable and specify it in as
the @code{old} parameter. Returns zero on and only on
success.

@item @code{xstrdup} [(@code{char* var, const char* original}) @arrow{} @code{int}]
@fnindex @code{xstrdup}
@cpindex Memory management
Wrapper for @code{strdup} that returns zero on and
only on success. @code{original} is duplicate and the
duplicate is stored in the variable @code{var}. If
@code{original} is @code{NULL}, @code{var} is set to
@code{NULL} and zero is returned.

@item @code{xmemdup} [(@code{void* var, const void* original, size_t elements, type}) @arrow{} @code{int}]
@fnindex @code{xmemdup}
@cpindex Memory management
Allocates a pointer of the type @code{type*} with
room for @code{elements} elements and stores the
pointer to @code{var}. If successful, the content of
@code{original} (@code{elements} elements of size
@code{sizeof(type*)}) is copied to @code{var}, and
zero is returned. On failure, a non-zero value is
returned.

@item @code{xperror} [(@code{const char* str}) @arrow{} @code{void}]
@fnindex @code{xperror}
@cpindex Error management
Invokes @code{perror(str)} if and only if @code{errno}
is non-zero and then sets @code{errno} to zero.
@code{str} should unless you have a specific reason
be @code{*argv}.

@item @code{fail_if} [(@code{condition}) @arrow{} @code{void}]
@fnindex @code{fail_if}
@cpindex Error management
If @code{condition} is satisfied, a jump is made to
the label @code{fail}. Additionally the location of
failure will be printed to standard error.

@item @code{exit_if} [(@code{condition, instructions}) @arrow{} @code{void}]
@fnindex @code{exit_if}
@cpindex Error management
@cpindex Terminating
If @code{condition} is satisfied, @code{instructions}
is invoked and @code{1} is @code{return}:ed.
@end table

@cpindex Signals
@sgindex @code{SIGDANGER}
@sgindex @code{SIGUPDATE}
@sgindex @code{SIGINFO}
Additionally, @file{<libmdsserver/macros.h>} defines
any missing signal name: currently @code{SIGDANGER},
@code{SIGINFO} and @code{SIGUPDATE}, and by inclusion
of @file{<libmdsserver/macro-bits.h>}, variants of
@code{atoi} for portability and convenience:

@cpindex Integer parsing macros
@table @code
@item atoz
@fnindex @code{atoz}
@tpindex @code{size_t}
Parse a human readable @code{const char*} 10-radix
integer to a @code{size_t}.

@item atosz
@fnindex @code{atosz}
@tpindex @code{ssize_t}
Parse a human readable @code{const char*} 10-radix
integer to a @code{ssize_t}.

@item atoh
@fnindex @code{atoh}
@tpindex @code{short int}
@tpindex @code{signed short int}
Parse a human readable @code{const char*} 10-radix
integer to a @code{short int}.

@item atouh
@fnindex @code{atouh}
@tpindex @code{unsigned short int}
Parse a human readable @code{const char*} 10-radix
integer to an @code{unsigned short int}.

@item atou
@fnindex @code{atou}
@tpindex @code{unsigned int}
Parse a human readable @code{const char*} 10-radix
integer to an @code{unsigned int}.

@item atoul
@fnindex @code{atoul}
@tpindex @code{unsigned long int}
Parse a human readable @code{const char*} 10-radix
integer to an @code{unsigned long int}.

@item atoull
@fnindex @code{atoull}
@tpindex @code{unsigned long long int}
Parse a human readable @code{const char*} 10-radix
integer to an @code{unsigned long long int}.

@item ato8
@fnindex @code{ato8}
@tpindex @code{int8_t}
Parse a human readable @code{const char*} 10-radix
integer to an @code{int8_t}.

@item atou8
@fnindex @code{atou8}
@tpindex @code{uint8_t}
Parse a human readable @code{const char*} 10-radix
integer to an @code{uint8_t}.

@item ato16
@fnindex @code{ato16}
@tpindex @code{int16_t}
Parse a human readable @code{const char*} 10-radix
integer to an @code{int16_t}.

@item atou16
@fnindex @code{atou16}
@tpindex @code{uint16_t}
Parse a human readable @code{const char*} 10-radix
integer to an @code{uint16_t}.

@item ato32
@fnindex @code{ato32}
@tpindex @code{int32_t}
Parse a human readable @code{const char*} 10-radix
integer to an @code{int32_t}.

@item atou32
@fnindex @code{atou32}
@tpindex @code{uint32_t}
Parse a human readable @code{const char*} 10-radix
integer to an @code{uint32_t}.

@item ato64
@fnindex @code{ato64}
@tpindex @code{int64_t}
Parse a human readable @code{const char*} 10-radix
integer to an @code{int64_t}.

@item atou64
@fnindex @code{atou64}
@tpindex @code{uint64_t}
Parse a human readable @code{const char*} 10-radix
integer to an @code{uint64_t}.

@item atoj
@fnindex @code{atoj}
@tpindex @code{intmax_t}
Parse a human readable @code{const char*} 10-radix
integer to an @code{intmax_t}.

@item atouj
@fnindex @code{atouj}
@tpindex @code{uintmax_t}
Parse a human readable @code{const char*} 10-radix
integer to an @code{uintmax_t}.
@end table



@node Auxiliary Functions
@section Auxiliary Functions

In the header file @file{<libmdsserver/util.h>},
libmdsserver defines common functions to help write
servers more concisely.

@table @asis
@item @code{parse_client_id} [(@code{const char* str}) @arrow{} @code{uint64_t}]
@fnindex @code{parse_client_id}
@cpindex Client ID, parsing
@cpindex Parsing client ID
Convert a client ID string into a client ID integer.

@item @code{getenv_nonempty} [(@code{const char* var}) @arrow{} @code{char*}]
@fnindex @code{getenv_nonempty}
@cpindex Environment variables, reading
@cpindex Reading environment variables
@cpindex Fetching environment variables
Read an environment variable, return @code{NULL} if
the variable's value is an empty string.

@item @code{prepare_reexec} [(@code{void}) @arrow{} @code{int}]
@fnindex @code{prepare_reexec}
@cpindex Re-executing servers
@cpindex Updating, online
@cpindex Online updating
@cpindex Version update
@sgindex @code{SIGUSR1}
@sgindex @code{SIGUPDATE}
Prepare the server so that it can re-execute into a
newer version of the executed file.

This is required for two reasons:

@enumerate 1
@item
We cannot use @code{argv[0]} as @env{PATH}-resolution
may cause it to reexec into another pathname, and
maybe to wrong program. Additionally @code{argv[0]}
may not even refer to the program, and @code{chdir}
could also hinter its use.

@item
The kernel appends @samp{ (deleted)} to
@file{/proc/self/exe} once it has been removed, so it
cannot be replaced.
@end enumerate

Returns zero on success and @code{-1} on error.

@item @code{reexec_server} [(@code{int argc, char** argv, int reexeced}) @arrow{} @code{void}]
@fnindex @code{reexec_server}
@cpindex Re-executing servers
@cpindex Updating, online
@cpindex Online updating
@cpindex Version update
@sgindex @code{SIGUSR1}
@sgindex @code{SIGUPDATE}
Re-execute the server. If @code{prepare_reexec}
failed or has not been called, @code{argv[0]} will be
used as a fallback. This functions has three input
parameters:

@table @code
@item argc
The number of elements in @code{argv}.
@item argv
The command line arguments.
@item reexeced
Whether the server has previously been re-executed.
@end table

This function only returns on failure.

@item @code{xsigaction} [(@code{int signo, void (*function)(int signo)}) @arrow{} @code{int}]
@fnindex @code{xsigaction}
@fnindex @code{sigaction}
@fnindex @code{signal}
@cpindex Signals
@code{sigaction} with the same parameters as
@code{signal}. This function should only be used for
common @command{mds} signals and signals that does
not require any special settings. This function may
choose to add additional behaviour depending on the
signal, such as blocking other signals. Returns zero
on success and @code{-1} on error.

@item @code{send_message} [(@code{int socket, const char* message, size_t length}) @arrow{} @code{size_t}]
@fnindex @code{send_message}
@cpindex Communication over sockets
@cpindex Socket communication
Send the message @code{messsage}, of length
@code{length} over the socket that is access with the
file descriptor @code{socket}. Returns the number of
bytes that have been sent, even on error.

@item @code{strict_atoi} [(@code{const char* str, int* value, int min, int max}) @arrow{} @code{int}]
@fnindex @code{strict_atoi}
@fnindex @code{atoi}
@cpindex Integer parsing
@cpindex Error management
A version of @code{atoi} that is strict about the
syntax and bounds. Parses the string @code{str} into
an @code{int} and stores it in @code{*value}. If the
string is not a 10-radix integer or has a value
outside [@code{min}, @code{max}], @code{-1} is
returned, otherwise zero is returned.

@item @code{full_write} [(@code{int fd, const char* buffer, size_t length}) @arrow{} @code{int}]
@fnindex @code{full_write}
@cpindex File writing
Send the buffer @code{buffer}, with the length
@code{length}, into the file whose file descriptor is
@code{fd} and ignores interruptions. Returns zero on
success and @code{-1} on error.

@item @code{full_read} [(@code{int fd, size_t* length}) @arrow{} @code{char*}]
@fnindex @code{full_read}
@cpindex File reading
Read the file whose file descriptor is @code{fd}
completely and ignore interruptions. If @code{length}
if not @code{NULL}, the length of the read file is
stored in @code{*length}. On success, the read
content is retured, on error @code{NULL} is returned.

@item @code{startswith_n} [(@code{const char*, const char*, size_t, size_t}) @arrow{} @code{int}]
@fnindex @code{startswith_n}
@cpindex String comparison
Check whether a string begins with a specific string,
where neither of the strings are necessarily
NUL-terminated. The parameters are:

@table @code
@item const char* haystack
The string that should start with the other string.
@item const char* needle
The string the first string should start with.
@item size_t haystack_n
The length of @code{haystack}.
@item size_t needle_n
The length of @code{needle}.
@end table

Returns 1 if @code{haystack} beings with
@code{needle}, otherwise zero is returned.

@item @code{uninterruptable_waitpid} [(@code{pid_t pid, int* restrict status, int options}) @arrow{} @code{pid_t}]
@fnindex @code{uninterruptable_waitpid}
@fnindex @code{waitpid}
@cpindex Process management
Wrapper around @code{waitpid} that never returns on an
interruption unless it is interrupted one hundred
times within the same clock second. The parameters
and return value are exactly those of @code{waitpid}.

@item @code{verify_utf8}[(@code{const char* string, int allow_modified_nul}) @arrow{} @code{int}]
@fnindex @code{verify_utf8}
@cpindex Security, encoding, UTF-8
@cpindex UTF-8, security
@cpindex Encoding, UTF-8, security
Checks whether a NUL-terminated string's encoding
matches UTF-8. This function will reject the string
if it does not use the shorted possible
byte-combination for each character. However, if
@code{allow_modified_nul} is set, it will allow
@code{192 128} in place of @code{0} for a
NUL-character.@footnote{Remember @code{0} is used
to terminated the string, but @code{192 128} is not.}
This function returns zero if the @code{string} is
properly formatted, and @code{-1} otherwise.
@end table



@node Data Structures
@section Data Structures

@cpindex Data structures
@cpindex Marshalling
@cpindex Serialisation
@cpindex Re-executing servers
@cpindex Updating, online
@cpindex Online updating
@cpindex Version update
@sgindex @code{SIGUSR1}
@sgindex @code{SIGUPDATE}
libmdsserver provides a small set of data structures
that are used by the @command{mds} servers. All of
these are written with marshal-functionallity.

@table @asis
@item @code{client_list_t} @{also known as @code{struct client_list}@}
@tpindex @code{client_list_t}
@tpindex @code{struct client_list}
@cpindex Client ID, lists
@cpindex Lists of client ID:s
In the header file
@file{<libmdsserver/client-list.h>}, libmdsserver
defines a dynamic list for storing client ID:s.

@item @code{linked_list_t} @{also known as @code{struct linked_list}@}
@tpindex @code{linked_list_t}
@tpindex @code{struct linked_list}
@cpindex Lists, linked
@cpindex Linked lists
In the header file
@file{<libmdsserver/linked-list.h>}, libmdsserver
defines a linear array sentinel doubly linked list.

@item @code{hash_table_t} @{also known as @code{struct hash_table}@}
@tpindex @code{hash_table_t}
@tpindex @code{struct hash_table}
@cpindex Tables, hash
@cpindex Maps, hash
@cpindex Dictionary, hash
@cpindex Hash table
In the header file @file{<libmdsserver/hash-table.h>},
libmdsserver defines a hash table.

@item @code{fd_table_t} @{also known as @code{struct fd_table}@}
@tpindex @code{fd_table_t}
@tpindex @code{struct fd_table}
@cpindex Tables, file descriptor
@cpindex Maps, file descriptor
@cpindex Dictionary, file descriptor
@cpindex File descriptor table
In the header file @file{<libmdsserver/fd-table.h>},
libmdsserver defines a lookup table for small
positive integer keys, intended as an alternative to
hash tables for file descriptors as keys.

@item @code{mds_message_t} @{also known as @code{struct mds_message}@}
@tpindex @code{mds_message_t}
@tpindex @code{struct mds_message}
@cpindex Message passing, data structure
In the header file
@file{<libmdsserver/mds-message.h>}, libmdsserver
defines a data structure for message between the
server or client and the master server, with the
capability of reading for a socket.
@end table

These data structures share a common set of associated
function. However, they do not use the same functions;
they are identical except they are are named with the
associated data structure. We will use @code{X_t} as
an example.

@table @asis
@item @code{X_destroy} [(@code{X_t* restrict this}) @arrow{} @code{void}]
@fnindex @code{client_list_destroy}
@fnindex @code{linked_list_destroy}
@fnindex @code{hash_table_destroy}
@fnindex @code{fd_table_destroy}
@fnindex @code{mds_message_destroy}
@cpindex Memory management
Releases all resouces in @code{*this}, @code{this}
itself is however not @code{free}:d.

However, @code{hash_table_destory} and
@code{fd_table_destory} have another signature.

@item @code{X_clone} [(@code{const X_t* restrict this, X_t* restrict out}) @arrow{} @code{int}]
@fnindex @code{client_list_clone}
@fnindex @code{linked_list_clone}
@fnindex @code{hash_table_clone}
@fnindex @code{fd_table_clone}
@fnindex @code{mds_message_clone}
@cpindex Memory management
Create a deep duplicate of @code{*this} and store it
in @code{*out}.

@item @code{X_marshal_size} [(@code{const X_t* restrict this}) @arrow{} @code{size_t}]
@fnindex @code{client_list_marshal_size}
@fnindex @code{linked_list_marshal_size}
@fnindex @code{hash_table_marshal_size}
@fnindex @code{fd_table_marshal_size}
@fnindex @code{mds_message_marshal_size}
@cpindex Marshalling
@cpindex Serialisation
@cpindex Re-executing servers
@cpindex Updating, online
@cpindex Online updating
@cpindex Version update
@sgindex @code{SIGUSR1}
@sgindex @code{SIGUPDATE}
Calculates the exact allocate size needed for the
parameter @code{data} in the function @code{X_marshal}
if called with the same @code{this} parameter.

@item @code{X_marshal} [(@code{const X_t* restrict this, char* restrict data}) @arrow{} @code{void}]
@fnindex @code{client_list_marshal}
@fnindex @code{linked_list_marshal}
@fnindex @code{hash_table_marshal}
@fnindex @code{fd_table_marshal}
@fnindex @code{mds_message_marshal}
@cpindex Marshalling
@cpindex Serialisation
@cpindex Re-executing servers
@cpindex Updating, online
@cpindex Online updating
@cpindex Version update
@sgindex @code{SIGUSR1}
@sgindex @code{SIGUPDATE}
Marshal the state of @code{*this} into @code{data}.
The number of bytes that will be stored (contiguously)
in @code{data} can be calculated with
@code{X_marshal_size}.

@item @code{X_unmarshal} [(@code{X_t* restrict this, char* restrict data)}) @arrow{} @code{int}]
@fnindex @code{client_list_unmarshal}
@fnindex @code{linked_list_unmarshal}
@fnindex @code{hash_table_unmarshal}
@fnindex @code{fd_table_unmarshal}
@fnindex @code{mds_message_unmarshal}
@cpindex Marshalling
@cpindex Serialisation
@cpindex Re-executing servers
@cpindex Updating, online
@cpindex Online updating
@cpindex Version update
@sgindex @code{SIGUSR1}
@sgindex @code{SIGUPDATE}
Unmarshal a @code{X_t} from @code{data} into
@code{*this}. Returns zero on success and @code{-1}
on error. The number of bytes read from @code{data}
should, if required, have been precalculated with
@code{X_marshal_size} and stored in an earlier
location of @code{data}.

However, @code{hash_table_unmarshal} and
@code{fd_table_unmarshal} have another signature.
@end table

@menu
* Client List::                     The @code{client_list_t} data structure.
* Linked List::                     The @code{linked_list_t} data structure.
* Tables::                          The @code{fd_table_t} and @code{hash_table_t} data structures.
* Message Structure::               The @code{mds_message_t} data structure.
@end menu



@page
@node Client List
@subsection Client List

@tpindex @code{client_list_t}
@tpindex @code{struct client_list}
@cpindex Client ID, lists
@cpindex Lists of client ID:s
@fnindex @code{client_list_create}
To create a client list, allocate a
@code{client_list_t*} or otherwise obtain a
@code{client_list_t*}, and call
@code{client_list_create} with that pointer as the
first argument, and the @code{0} as the second
argument, unless you want to tune the initialisation.
@code{client_list_create} will return zero on and
only on successful initialisation.
@code{client_list_create}'s second parameter ---
@code{size_t capacity} --- can be used to specify how
many element the list should initially fit. It will
grow when needed, but it is a good idea to tell it
how many elements you are planning to populate it
with.

@code{client_list_t} has two associated functions for
manipulating its content:

@table @asis
@item @code{client_list_add} [(@code{client_list_t* restrict this, uint64_t client}) @arrow{} @code{int}]
@fnindex @code{client_list_add}
This function will add the element @code{client} to
the list @code{*this}, and return zero on and only on
success.

@item @code{client_list_remove} [(@code{client_list_t* restrict this, uint64_t client}) @arrow{} @code{void}]
@fnindex @code{client_list_remove}
This function will remove exactly one occurrence,
provided that there is at least on occurrence, of the
element @code{client} for the list @code{*this}.
@end table

To retrieve the number elements stored in a list,
reads its variable @code{size_t size}. The variable
@code{uint64_t* clients} is used to retrieve stored
elements.

@ifset AFOURPAPER_OR_USLETTER_OR_SMALLBOOK_WITH_SMALLFONT
@example
void print_elements(client_list_t* this)
@{
  size_t i;
  for (i = 0; i < this->size; i++)
    printf("Element #%zu: %" PRIu64 "\n", i, this->elements[i]);
@}
@end example
@end ifset
@ifclear AFOURPAPER_OR_USLETTER_OR_SMALLBOOK_WITH_SMALLFONT
@example
void print_elements(client_list_t* this)
@{
  size_t i;
  for (i = 0; i < this->size; i++)
    printf("Element #%zu: %" PRIu64 "\n",
           i, this->elements[i]);
@}
@end example
@end ifclear



@node Linked List
@subsection Linked List

@tpindex @code{linked_list_t}
@tpindex @code{struct linked_list}
@cpindex Lists, linked
@cpindex Linked lists
@code{linked_list_t} is a linear array sentinel
doubly linked list. This means that is implemented
using arrays rather than node references. More
specifically, since it is doubly linked@footnote{And
not using XOR-linking.}, it is implemented using
three arrays:

@table @asis
@item @code{values} [@code{size_t*}]
The value stored in each node.

@item @code{next} [@code{ssize_t*}]
The next node for each node, @code{edge} if the
current node is the last node, and
@code{LINKED_LIST_UNUSED} if there is no node on this
position.

@item @code{previous} [@code{ssize_t*}]
The previous node for each node, @code{edge} if the
current node is the first node, and
@code{LINKED_LIST_UNUSED} if there is no node on this
position.
@end table

The linked list has a sentinel node that joins boths
ends of the list. The index of this node is stored in
the variable @code{edge}.

@cpindex Memory management
@fnindex @code{linked_list_pack}
Because the list is implemented using arrays, if the
number of elements in it shinks considerably, it will
not be able to automatically free unused space.
Instead you must call @code{linked_list_pack}:

@table @asis
@item @code{linked_list_pack} [(@code{linked_list_t* restrict this}) @arrow{} @code{int}]
Pack the list so that there are no reusable positions,
and reduce the capacity to the smallest capacity that
can be used. Note that values (nodes) returned by the
list's methods will become invalid. Additionally (to
reduce the complexity) the list will be defragment so
that the nodes' indices are continuous. This method
has linear time complexity and linear memory
complexity.
@end table

@fnindex @code{linked_list_create}
To create a linked list list, allocate a
@code{linked_list_t*} or otherwise obtain a
@code{linked_list_t*}, and call
@code{linked_list_create} with that pointer as the
first argument, and the @code{0} as the second
argument, unless you want to tune the initialisation.
@code{linked_list_create} will return zero on and
only on successful initialisation.
@code{linked_list_create}'s second parameter ---
@code{size_t capacity} --- can be used to specify how
many element the list should initially fit. It will
grow when needed, but it is a good idea to tell it
how many elements you are planning to populate it
with.

There are five functions adding and removing items to
and from a linked list:

@table @asis
@item @code{linked_list_insert_after} [(@code{this, size_t value, ssize_t predecessor}) @arrow{} @code{ssize_t}]
@fnindex @code{linked_list_insert_after}
Create a new node with the value @code{value} and add
it to the list @code{*this} after the node
@code{predecessor}. On success, the new node is
returned, on failure @code{LINKED_LIST_UNUSED} is
returned.

@item @code{linked_list_insert_before} [(@code{this, size_t value, ssize_t successor}) @arrow{} @code{ssize_t}]
@fnindex @code{linked_list_insert_before}
Create a new node with the value @code{value} and add
it to the list @code{*this} before the node
@code{successor}. On success, the new node is
returned, on failure @code{LINKED_LIST_UNUSED} is
returned.

@item @code{linked_list_remove_after} [(@code{this, ssize_t predecessor}) @arrow{} @code{ssize_t}]
@fnindex @code{linked_list_remove_after}
Remove and return the node in the list @code{*this}
directly after the node @code{predecessor}.

@item @code{linked_list_remove_before} [(@code{this, ssize_t successor}) @arrow{} @code{ssize_t}]
@fnindex @code{linked_list_remove_before}
Remove and return the node in the list @code{*this}
directly before the node @code{predecessor}.

@item @code{linked_list_remove} [(@code{this, ssize_t node}) @arrow{} @code{void}]
@fnindex @code{linked_list_remove}
Remove the node @code{node} from the list
@code{*this}.
@end table

The data type for @code{this} is @code{linked_list_t*}
with the @code{restrict} modifier for these and all
other @code{linked_list_t} functions.

Note that if the node @code{this->edge} is removed,
the list become circularly linked and the sentinel
will become missing which renders invokation of all
macros undefined in behaviour. Further note that
removing the sentinel while it is the only node in
the list invokes undefined behaviour. Also note that
addressing non-existing nodes invokes undefined
behaviour.

@file{<libmdsserver/linked_list.h>} defines two
macros for inserting nodes at the edges of a linked
list and two macros for removing nodes from the edges
of a linked list:

@table @asis
@item @code{linked_list_insert_beginning} [(@code{linked_list_t* this, size_t value}) @arrow{} @code{ssize_t}]
@fnindex @code{linked_list_insert_beginning}
Create a new node with the value @code{value} in
insert it to the beginning of the list @code{*this}.
On success, the new node is returned, on failure
@code{LINKED_LIST_UNUSED} is returned.

@item @code{linked_list_insert_end} [(@code{linked_list_t* this, size_t value}) @arrow{} @code{ssize_t}]
@fnindex @code{linked_list_insert_end}
Create a new node with the value @code{value} in
insert it to the end of the list @code{*this}. On
success, the new node is returned, on failure
@code{LINKED_LIST_UNUSED} is returned.

@item @code{linked_list_remove_beginning} [(@code{linked_list_t* this}) @arrow{} @code{ssize_t}]
@fnindex @code{linked_list_remove_beginning}
Remove and return the first node in the list
@code{*this}.

@item @code{linked_list_remove_end} [(@code{linked_list_t* this}) @arrow{} @code{ssize_t}]
@fnindex @code{linked_list_remove_end}
Remove and return the node node in the list
@code{*this}.
@end table

Additionally the library defines a macro that wrappes
the @code{for} keyword to iterate over all nodes
(except the sentinel node) the a linked list:

@table @asis
@item @code{foreach_linked_list_node} [(@code{linked_list_t this, ssize_t node})]
@fnindex @code{foreach_linked_list_node}
Wrapper for `for` keyword that iterates over each
element in the list @code{this}, and store the
current node to the variable named by the parameter
@code{node} for each iterations.

@example
void print_linked_list_values(linked_list_t* list)
@{
  ssize_t node;
  foreach_linked_list_node (*list, node)
    printf("%zi\n", list->values[node]);
@}
@end example

Note that the data type for @code{this} in the macro
is not a pointer.
@end table

There is also a function intended for debugging:

@table @asis
@item @code{linked_list_dump} [(@code{linked_list_t* restrict this, FILE* restrict output}) @arrow{} @code{void}]
@fnindex @code{linked_list_dump}
The all internal data of the list @code{*this} into
the stream @code{output}.
@end table



@node Tables
@subsection Tables

@tpindex @code{fd_table_t}
@tpindex @code{struct fd_table}
@cpindex Tables, file descriptor
@cpindex Maps, file descriptor
@cpindex Dictionary, file descriptor
@cpindex File descriptor table
@tpindex @code{hash_table_t}
@tpindex @code{struct hash_table}
@cpindex Tables, hash
@cpindex Maps, hash
@cpindex Dictionary, hash
@cpindex Hash table
libmdsserver defines two similar data structures:
@code{fd_table_t} and @code{hash_table_t}. Whenever a
function exists for both data structures we will
write @code{X_table} instead of @code{fd_table} and
@code{hash_table}. Additionally, unless otherwise
stated, a function's parameter named @code{this} will
be of the type @code{hash_table_t*} if the function's
name start with @code{hash_table} and
@code{fd_table_t*} if the function's name start with
@code{fd_table}, with the @code{restrict} modifier.

@table @asis
@item @code{X_table_create} [(@code{this}) @arrow{} @code{int}]
@fnindex @code{hash_table_create}
@fnindex @code{fd_table_create}
Initialises @code{*this} so it can be used as a
table. Returns zero on and only on success.

These functions are defined as macros.

@item @code{X_table_create_tuned} [(@code{this, size_t initial_capacity}) @arrow{} @code{int}]
@fnindex @code{hash_table_create_tuned}
@fnindex @code{fd_table_create_tuned}
Initialises @code{*this} so it can be used as a
table, and makes its initial capacity at least
@code{initial_capacity}. Returns zero on and only on
success.

@code{hash_table_create_tuned} is defined as a macro.

@item @code{hash_table_create_fine_tuned} [(@code{this, size_t initial_capacity, float load_factor}) @arrow{} @code{int}]
@fnindex @code{hash_table_create_fine_tuned}
Initialises @code{*this} so it can be used as a
table, and makes its initial capacity at least
@code{initial_capacity} and its load factor
@code{load_factor}. Returns zero on and only on
success.

@item @code{X_table_destroy} [(@code{this, free_func* key_freer, free_func* value_freer}) @arrow{} @code{void}]
@fnindex @code{hash_table_destroy}
@fnindex @code{fd_table_destroy}
Release all resources in the table @code{*this}, but
do not @code{free} @code{this} itself. Should be
called even if construction fails. If
@code{keys_freer} is not @code{NULL}, this function
will be called for each key. If @code{values_freer}
is not @code{NULL}, this function will be called for
each value.

@item @code{X_table_contains_value} [(@code{const this, size_t value}) @arrow{} @code{int}]
@fnindex @code{hash_table_contains_value}
@fnindex @code{fd_table_contains_value}
Check whether the value @code{value} is stored in the
table @code{*this}.

@item @code{X_table_contains_key} [(@code{const this, key}) @arrow{} @code{int}]
@fnindex @code{hash_table_contains_key}
@fnindex @code{fd_table_contains_key}
Check whether the key @code{code} is used in the
table @code{*this}.

The data type for the parameter @code{key} is
@code{size_t} for @code{hash_table} and @code{int}
for @code{fd_table}.

@item @code{X_table_get} [(@code{const this, key}) @arrow{} @code{size_t}]
@fnindex @code{hash_table_get}
@fnindex @code{fd_table_get}
Look up a value by its key @code{key} in the table
@code{*this}. Zero will be returned if the key was
not used.

@item @code{hash_table_get_entry} [(@code{const this, size_t key}) @arrow{} @code{hash_entry_t*}]
@fnindex @code{hash_table_get_entry}
Look up an entry by its key @code{key} in the table
@code{*this}. @code{NULL} will be returned if the key
was not used.

@item @code{X_table_put} [(@code{this, key, size_t value}) @arrow{} @code{size_t}]
@fnindex @code{hash_table_put}
@fnindex @code{fd_table_put}
Map the value @code{value} to the key @code{key} in
the talbe @code{*this}. If a value was already mapped
to the key, that value will be returned, otherwise
zero will be returned. Zero will also be returned on
error. @code{errno} will be set to zero on and only
on success.

The data type for the parameter @code{key} is
@code{size_t} for @code{hash_table} and @code{int}
for @code{fd_table}.

@item @code{X_table_remove} [(@code{this, key}) @arrow{} @code{size_t}]
@fnindex @code{hash_table_remove}
@fnindex @code{fd_table_remove}
Unmaps the key @code{key} for the table @code{*this}.
If a value was mapped to the key, that value will be
returned, otherwise zero will be returned.

The data type for the parameter @code{key} is
@code{size_t} for @code{hash_table} and @code{int}
for @code{fd_table}.

@item @code{X_table_clear} [(@code{this}) @arrow{} @code{void}]
@fnindex @code{hash_table_clear}
@fnindex @code{fd_table_clear}
Unmaps all keys in the table @code{*this}.

@item @code{X_table_unmarshal} [(@code{this, char* restrict data, remap_func* remapper}) @arrow{} @code{int}]
@fnindex @code{hash_table_unmarshal}
@fnindex @code{fd_table_unmarshal}
As described in @ref{Data Structures} but with one
additional parameter: @code{remapper}. If this
parameter is not @code{NULL} this function is used to
edit values. It will be called once for each value
and the output of the function will be used inplace
of the input value.
@end table

@file{<libmdsserver/hash-table.h>} also defines as
wrapper macro for the @code{for} keyword:

@table @asis
@item @code{foreach_hash_table_entry} [(@code{hash_table_t this, size_t i, hash_entry_t* entry})]
@fnindex @code{foreach_hash_table_entry}
Iterates over entry element in the hash table
@code{*this}. On each iteration, the entry will be
stored to the variable @code{entry} and the bucket
index will be stored to the variable @code{i}.

@ifset AFOURPAPER_OR_USLETTER_OR_SMALLBOOK_WITH_SMALLFONT
@example
void print_hash_table(hash_table_t* table)
@{
  hash_entry_t* entry;
  size_t i;
  foreach_hash_table_entry (*table, i, entry)
    printf("%zu --> %zu\n", entry->key, entry->value);
@}
@end example
@end ifset
@ifclear AFOURPAPER_OR_USLETTER_OR_SMALLBOOK_WITH_SMALLFONT
@example
void print_hash_table(hash_table_t* table)
@{
  hash_entry_t* entry;
  size_t i;
  foreach_hash_table_entry (*table, i, entry)
    printf("%zu --> %zu\n", entry->key,
                            entry->value);
@}
@end example
@end ifclear

Note the the data type for the parameter @code{this}
is not a popinter.
@end table

@vrindex @code{value_comparator}
@vrindex @code{hash_table_t.value_comparator}
@vrindex @code{fd_table_t.value_comparator}
The structures @code{hash_table_t} and
@code{fd_table_t} contain the variable
@code{value_comparator} which by default is
@code{NULL}@. If this variable is set to @code{NULL},
two values will be considered equal if and only if
they are numerically identical; otherwise two values
will be considered equal if and only if
@code{value_comparator} returned a non-zero value if
those two values are used for the function's
arguments. The data type for @code{value_comparator}
is @code{compare_func*}.

@code{hash_table_t} also contains two other variables:

@table @asis
@item @code{key_comparator} [@code{compare_func*}]
@vrindex @code{ket_comparator}
@vrindex @code{hash_table_t.ket_comparator}
Identical to @code{value_comparator}, except it is
used for keys rather the values.

@item @code{hasher} [@code{hash_func*}]
@vrindex @code{hasher}
@vrindex @code{hash_table_t.hasher}
By default, the hash value for key is identical to
the key itself. However, if this variable is not
@code{NULL}, it will be used to calculate the hash
value for keys.
@end table

@tpindex @code{hash_entry_t}
@tpindex @code{struct hash_entry}
There is a secondary data structure defined for hash
tables: @code{hash_entry_t} @{also known as
@code{struct hash_entry}@}. It is the data structure
used for entries in a hash table. @code{hash_entry_t}
contain three variables you may be interested in:

@table @asis
@item @code{key} [@code{size_t}]
The key.

@item @code{value} [@code{size_t}]
The value associated with the key.

@item @code{hash} [@code{size_t}]
The hash value of the key.
@end table

By inclusion of @file{<libmdsserver/table-common.h>},
@file{<libmdsserver/hash-table.h>} and
@file{<libmdsserver/fd-table.h>} defines four
@code{typedef}:s for function signatures:

@table @asis
@item @code{compare_func} [(@code{size_t a, size_t b}) @arrow{} @code{int}]
@tpindex @code{compare_func}
A function that performs a comparison of two objects.
Should return non-zero if and only if @code{a} and
@code{b} are to be considered equal in the given
context.

@item @code{hash_func} [(@code{size_t value}) @arrow{} @code{size_t}]
@tpindex @code{hash_func}
A function that hashes an object or a value. Should
return the hash value for @code{value}.

@item @code{free_func} [(@code{size_t obj}) @arrow{} @code{void}]
@tpindex @code{free_func}
A function that, to the extent that is appropriate,
releases the object @code{obj}'s resources and
@code{free}:s it.

@item @code{remap_func} [(@code{size_t obj}) @arrow{} @code{size_t}]
@tpindex @code{remap_func}
A function that translates a object into a new object.
The function should return new object that should
replace the object @code{obj}.
@end table

If you are working with strings, you may consider
including the header file
@file{<libmdsserver/hash-help.h>}. It defines to
useful functions:

@table @asis
@item @code{string_hash} [(@code{const char* str}) @arrow{} @code{size_t}]
@fnindex @code{string_hash}
Calculate and returns the hash value of the string
@code{str}.

@item @code{string_comparator} [(@code{char* str_a, char* str_b}) @arrow{} @code{int}]
@fnindex @code{string_comparator}
@cpindex String comparison
Returns non-zero if either both @code{str_a} and
@code{str_b} are @code{NULL} or neither are
@code{NULL} but are identical strings by content upto
their first NUL characters (or by address).
@end table

These functions are defined as pure and
@code{static inline}.



@node Message Structure
@subsection Message Structure

@tpindex @code{mds_message_t}
@tpindex @code{struct mds_message}
@cpindex Message passing, data structure
Apart from internal data @code{mds_message_t}
contains four variables:

@table @asis
@item @code{headers} [@code{char**}]
The headers in the message, each element in this list
as an unparsed header, it consists of both the header
name and its associated value, joined by `: '. A
header cannot be @code{NULL} (unless its memory
allocation failed,) but @code{headers} itself is
@code{NULL} if there are no headers. The `Length'
header should be included in this list.

@item @code{header_count} [@code{size_t}]
The number of headers in the message.

@item @code{payload} [@code{char*}]
The payload of the message, @code{NULL} if none (of
zero-length).

@item @code{payload_size} [@code{size_t}]
The length of the message's payload. This value will
be the same as the value of the @code{Length} header.
@end table

There are six functions specific to
@code{mds_message_t}. The @code{this}-parameter's
data type for this functions are @code{mds_message_t*}
with the @code{restrict} modifier.

@table @asis
@item @code{mds_message_initialise} [(@code{this}) @arrow{} @code{int}]
@fnindex @code{mds_message_initialise}
Initialises @code{*this} so that it can be used by
@code{mds_message_read}. Returns zero on and only on
success. On failure you should destroy @code{*this}
using @code{mds_message_destroy}.

@item @code{mds_message_zero_initialise} [(@code{this}) @arrow{} @code{void}]
@fnindex @code{mds_message_zero_initialise}
This function is similar to
@code{mds_message_initialise}, however it cannot fail
and thus have no return value. The difference it is
action is that it will not allocate an internal
buffer.

@item @code{mds_message_extend_headers} [(@code{this, size_t extent}) @arrow{} @code{int}]
@fnindex @code{mds_message_extend_headers}
Ensures that @code{extent} additional headers can be
stored in the @code{*this}. Returns zero on and only
on success.

@item @code{mds_message_read} [(@code{this, int fd}) @arrow{} @code{int}]
@fnindex @code{mds_message_read}
Reads the next message from the socket file descriptor
@code{fd} and stores it in @code{*this}. Returns zero
on success and non-zero on error or interruption.
@code{*this} should be destroyed using
@code{mds_message_destroy} on error but not on
interruption. If @code{-2} is returned @code{errno}
will not have been set; @code{-2} indicates that the
message is malformated, which is a state that cannot
be recovered from.

@item @code{mds_message_compose_size} [(@code{const this}) @arrow{} @code{size_t}]
@fnindex @code{mds_message_compose_size}
This function is to @code{mds_message_compose} as
@code{mds_message_marshal_size} is to
@code{mds_message_marshal}.

@item @code{mds_message_compose} [(@code{const this, char* restrict data}) @arrow{} @code{void}]
@fnindex @code{mds_message_compose}
This function is similar to
@code{mds_message_marshal}. The only difference is
that it will not store internal data and instead
create a message that can be broadcasted in the
display server message passing system.
@end table



@node mds-base.o
@chapter @file{mds-base.o}

@cpindex @file{mds-base}
@file{mds-base.c} and @file{mds-base.h} as an object
filepair whose purpose is similar to libmdsserver.
@file{mds-base} is compiled into all @command{mds}
servers and implements common procedures including
@code{main}. It also complements procedures that are
weakly defined, that is, if the server implementation
also defines them, the server implementations
procedure replaces @file{mds-base}'s implementation at
compile-time.

@file{mds-base} defines one function that you can
call from threads you create and functions that should
be implement depending on specified conditions:

@table @asis
@item @code{trap_signals} [(@code{void}) @arrow{} @code{int}]
@fnindex @code{trap_signals}
@cpindex Signals
Set up signal traps for all especially handled
signals. Returns zero on and only on success.
@end table

@file{mds-base} weakly defines functions that you can
replace if they do not suit your needs:

@table @asis
@item @code{parse_cmdline} [(@code{void}) @arrow{} @code{int}]
@fnindex @code{parse_cmdline}
@cpindex Parse command line
@cpindex Command line, parse
Parses command line arguments. Returns zero on and
only on success.

This function will parse the following options:

@table @option
@item --initial-spawn
@opindex @option{--initial-spawn}
It is the first time the server is spawn by its
spawner process.

@item --respawn
@opindex @option{--respawn}
The server was respawned.

@item --re-exec
@opindex @option{--re-exec}
The server is re-executing.

@item --alarm=SECONDS
@opindex @option{--alarm}
@sgindex @code{SIGALRM}
Kill the process after @var{SECONDS} seconds. At most
one minute.

@item --on-init-fork
@opindex @option{--on-init-fork}
Fork the process to detach it from its parent when
the server has been initialised.

@item --on-init-sh=COMMAND
@opindex @option{--on-init-sh}
When the server has been initialised, run the command
@var{COMMAND}@.

@item --immortal
@opindex @option{--immortal}
The server should do its best not to die. For example
do not die if @code{SIGDANGER} is received even if
that is the server's default action.
@end table

@item @code{connect_to_display} [(@code{void}) @arrow{} @code{int}]
@fnindex @code{connect_to_display}
@cpindex Connecting to the display
Connects to the display. Returns zero on and only on
success.

@item @code{server_initialised} [(@code{void}) @arrow{} @code{int}]
@fnindex @code{server_initialised}
@cpindex Initialisation
This function should be called when the server has
been properly initialised but before initialisation
of anything that is removed at forking is initialised.
Returns zero on and only on success.

@item @code{signal_all} [(@code{int signo}) @arrow{} @code{void}]
@fnindex @code{signal_all}
@cpindex Signals, multi-threading
@cpindex Multi-threading, signals
@cpindex Treading, signals
This function should be implemented by the actual
server implementation if the server is multi-threaded.
It sends the singal @code{signo} to all threads
except the current thread.

@item @code{received_danger} [(@code{int signo}) @arrow{} @code{void}]
@fnindex @code{received_danger}
@sgindex @code{SIGDANGER}
@vrindex @code{server_characteristics.danger_is_deadly}
@vrindex @code{danger_is_deadly}
@cpindex Memory release, automatic
@cpindex Memory release, forced
@cpindex Automated memory release
@cpindex Forcing memory release
@cpindex Releasing memory
@vrindex @code{danger}
This function is called when a signal that signals the
system is running out of memory has been received.
The exact received signal is specified by the
parameter @code{signo}. When this function is
invoked, the server should free up all memory it can
spare. When this function is invoked, it should set
the variable @code{danger} to a non-zero value. If
@code{server_characteristics.danger_is_deadly} is set,
this function will never be called.

@item @code{received_reexec} [(@code{int signo}) @arrow{} @code{void}]
@fnindex @code{received_reexec}
@vrindex @code{reexecing}
@vrindex @code{terminating}
@cpindex Re-executing servers
@cpindex Updating, online
@cpindex Online updating
@cpindex Version update
@sgindex @code{SIGUSR1}
@sgindex @code{SIGUPDATE}
This function is called when a signal that signals the
server to re-execute has been received. The exact
received signal is specified by the parameter
@code{signo}. When this function is invoked, it
should set the variables @code{reexecing} and
@code{terminating} to a non-zero value.

@item @code{received_terminate} [(@code{int signo}) @arrow{} @code{void}]
@fnindex @code{received_terminate}
@vrindex @code{terminating}
@cpindex Terminating
@sgindex @code{SIGTERM}
@sgindex @code{SIGINT}
This function is called when a signal that signals the
server to terminate has been received. The exact
received signal is specified by the parameter
@code{signo}. When this function is invoked, it
should set the variable @code{terminating} to a
non-zero value.

@item @code{received_info} [(@code{int signo}) @arrow{} @code{void}]
@fnindex @code{received_info}
@sgindex @code{SIGINFO}
@cpindex State dump
@cpindex Statistics dump
This function is called when a signal that signals the
server to dump state information and statistics has
been received. The exact received signal is specified
by the parameter @code{signo}.

@item @code{fork_cleanup} [(@code{int status}) @arrow{} @code{void}]
@fnindex @code{fork_cleanup}
@vrindex @code{server_characteristics.fork_for_safety}
@vrindex @code{fork_for_safety}
@cpindex Initialisation
This function should be implemented by the actual
server implementation if the server has set
@code{server_characteristics.fork_for_safety} to be a
non-zero value. This function is called by the parent
server process when the child server process exits,
if the server has completed its initialisation. The
parameter @code{status} specifies the child process
exit status as returned by @code{waitpid}.
@end table

Additionally, @file{mds-base} expects the server
implementation to define and implement a set of
functions:

@table @asis
@item @code{preinitialise_server} [(@code{void}) @arrow{} @code{int}]
@fnindex @code{preinitialise_server}
@fnindex @code{initialise_server}
@fnindex @code{unmarshal_server}
@cpindex Initialisation
This function will be invoked before
@code{initialise_server} (if not re-executing) or
before @code{unmarshal_server} (if not re-executing).
Returns zero on and only on success.

@item @code{initialise_server} [(@code{void}) @arrow{} @code{int}]
@fnindex @code{initialise_server}
@cpindex Initialisation
This function should initialise the server. It not
invoked after a re-execution. Returns zero on and
only on success.

@item @code{postinitialise_server} [(@code{void}) @arrow{} @code{int}]
@fnindex @code{postinitialise_server}
@fnindex @code{initialise_server}
@fnindex @code{unmarshal_server}
@cpindex Initialisation
This function will be invoked after
@code{initialise_server} (if not re-executing) or
after @code{unmarshal_server} (if re-executing).
Returns zero on and only on success.

@item @code{marshal_server_size} [(@code{void}) @arrow{} @code{size_t}, pure]
@fnindex @code{marshal_server_size}
@fnindex @code{marshal_server}
@cpindex Re-executing servers
@cpindex Updating, online
@cpindex Online updating
@cpindex Version update
@sgindex @code{SIGUSR1}
@sgindex @code{SIGUPDATE}
Calculate and returns the number of bytes that will
be stored by @code{marshal_server}. On failure the
server should call @code{abort} or exit with failure
status by other means. However it should not be
possible for this function to fail.
@code{marshal_server_size} must be pure@footnote{That
is, define with and conforming to
@code{__attribute__((pure))}.}.

@item @code{marshal_server} [(@code{char* state_buf}) @arrow{} @code{int}]
@fnindex @code{marshal_server}
@cpindex Re-executing servers
@cpindex Updating, online
@cpindex Online updating
@cpindex Version update
@sgindex @code{SIGUSR1}
@sgindex @code{SIGUPDATE}
Marshal server implementation specific data into the
buffer @code{state_buf}. Returns zero on and only on
success.

@item @code{unmarshal_server} [(@code{char* state_buf}) @arrow{} @code{int}]
@fnindex @code{unmarshal_server}
@cpindex Re-executing servers
@cpindex Updating, online
@cpindex Online updating
@cpindex Version update
@sgindex @code{SIGUSR1}
@sgindex @code{SIGUPDATE}
Unmarshal server implementation specific data from the
buffer @code{state_buf} and update the servers state
accordingly. Returns zero on and only on success.

@fnindex @code{reexec_failure_recover}
On critical failure the program should call
@code{abort} or exit with failure status by other
means. That is, do not let
@code{reexec_failure_recover} run successfully, if it
unrecoverable error has occurred or one severe enough
that it is better to simply respawn.

@item @code{reexec_failure_recover} [(@code{void}) @arrow{} @code{int}]
@fnindex @code{reexec_failure_recover}
@cpindex Re-executing servers
@cpindex Updating, online
@cpindex Online updating
@cpindex Version update
@sgindex @code{SIGUSR1}
@sgindex @code{SIGUPDATE}
Attempt to recover from a re-execution failure that
has been detected after the server successfully
updated it execution image. Returns zero on and only
on success.

@item @code{master_loop} [(@code{void}) @arrow{} @code{int}]
@fnindex @code{master_loop}
@cpindex Initialisation
Perform the server's mission. Returns zero on and
only on success.
@end table

@file{mds-base} also defines a number of global
variables.

@table @asis
@item @code{argc} [@code{int}]
@vrindex @code{argc}
@cpindex Command line
Number of elements in @code{argv}.

@item @code{argv} [@code{char**}]
@vrindex @code{argv}
@cpindex Command line
Command line arguments.

@item @code{is_respawn} [@code{int}]
@vrindex @code{is_respawn}
@cpindex Initialisation
@vrindex @code{is_reexec}
Whether the server has been respawn rather than this
being the initial spawn. This will be at least as true
as @code{is_reexec}.

@item @code{is_reexec} [@code{int}]
@vrindex @code{is_reexec}
@cpindex Initialisation
@cpindex Re-executing servers
@cpindex Updating, online
@cpindex Online updating
@cpindex Version update
@sgindex @code{SIGUSR1}
@sgindex @code{SIGUPDATE}
Whether the server is continuing from a
self-reexecution.

@item @code{is_immortal} [@code{int}]
@vrindex @code{is_immortal}
@opindex @option{--immortal}
Whether the server should do its best to resist event
triggered death.

@item @code{on_init_fork} [@code{int}]
@vrindex @code{on_init_fork}
@cpindex Initialisation
Whether to fork the process when the server has been
properly initialised.

@item @code{on_init_sh} [@code{char*}]
@vrindex @code{on_init_sh}
@cpindex Initialisation
Command the run (@code{NULL} for none) when the server
has been properly initialised.

@item @code{master_thread} [@code{pthread_t}]
@vrindex @code{master_thread}
@cpindex Threading
@cpindex Multi-threading
The thread that runs the master loop.

@item @code{terminating} [@code{volatile sig_atomic_t}]
@vrindex @code{terminating}
@cpindex Terminating
Whether the server has been signaled to terminate.

@item @code{reexecing} [@code{volatile sig_atomic_t}]
@vrindex @code{reexecing}
@cpindex Initialisation
@cpindex Re-executing servers
@cpindex Updating, online
@cpindex Online updating
@cpindex Version update
Whether the server has been signaled to re-execute.

@item @code{danger} [@code{volatile sig_atomic_t}]
@vrindex @code{danger}
@sgindex @code{SIGDANGER}
@cpindex Memory release, automatic
@cpindex Memory release, forced
@cpindex Automated memory release
@cpindex Forcing memory release
@cpindex Releasing memory
Whether the server has been signaled to free unneeded
memory.

@item @code{socket_fd} [@code{int}]
@vrindex @code{socket_fd}
@cpindex Connecting to the display
The file descriptor of the socket that is connected
to the server.
@end table

@cpindex Server characteristics
@file{mds-base} expects the server implementation to
define a variable that specifies how @file{mds-base}
should behave:

@table @asis
@item @code{server_characteristics} [@code{server_characteristics_t}]
@vrindex @code{server_characteristics}
This variable should declared by the actual server
implementation. It must be configured before
@code{main} is invoked. That is, it should be
configured by a constructor. If it is configured at
its definition, it is configured by a constructor;
that is normally how you want to configured it.
@end table

@tpindex @code{server_characteristics_t}
@tpindex @code{struct server_characteristics}
@code{server_characteristics_t} @{also known as
@code{struct server_characteristics}@} is a packed
@footnote{That is, define with @code{__attribute__((packed))}.} with the following fields:

@table @asis
@item @code{require_privileges} [@code{unsigned : 1}]
@vrindex @code{require_privileges}
@cpindex Previleges
@cpindex Security, previleges
Setting this to zero will cause the server to drop
privileges as a security precaution.

@item @code{require_display} [@code{unsigned : 1}]
@vrindex @code{require_display}
@cpindex Connecting to the display
Setting this to non-zero will cause the server to
connect to the display.

@item @code{require_respawn_info} [@code{unsigned : 1}]
@vrindex @code{require_respawn_info}
@opindex @option{--initial-spawn}
@opindex @option{--respawn}
@cpindex Initialisation
Setting this to non-zero will cause the server to
refuse to start unless either @option{--initial-spawn}
or @option{--respawn} is used.

@item @code{sanity_check_argc} [@code{unsigned : 1}]
@vrindex @code{sanity_check_argc}
@cpindex Command line, security
@cpindex Security, command line
Setting this to non-zero will cause the server to
refuse to start if there are too many command line
arguments.

@item @code{fork_for_safety} [@code{unsigned : 1}]
@vrindex @code{fork_for_safety}
@cpindex Initialisation
@fnindex @code{fork_cleanup}
Setting this to non-zero will cause the server to
place itself in a fork of itself when initialised.
This can be used to let the server clean up fatal
stuff after itself if it crashes. When the child
exits, no matter how it exits, the parent will call
@code{fork_cleanup} and then die in the same manner
as the child.

@item @code{danger_is_deadly} [@code{unsigned : 1}]
@vrindex @code{danger_is_deadly}
@sgindex @code{SIGDANGER}
@vrindex @code{fork_for_safety}
@fnindex @code{server_initialised}
@cpindex Memory release, automatic
@cpindex Memory release, forced
@cpindex Automated memory release
@cpindex Forcing memory release
@cpindex Releasing memory
Setting this to non-zero without setting a signal
action for @code{SIGDANGER} will cause the server to
die if @code{SIGDANGER} is received. It is safe to
set both @code{danger_is_deadly} and
@code{fork_for_safety} to non-zero, during the call
of @code{server_initialised} the signal handler for
@code{SIGDANGER} in the parent process will be set to
@code{SIG_IGN} independently of the value of
@code{danger_is_deadly} if @code{fork_for_safety} is
set to non-zero.

@opindex @option{--immortal}
This setting will be treated as set to zero if
@option{--immortal} is used.
@end table



@node Keyboard Codes
@chapter Keyboard Codes

@cpindex Scancodes
Keyboard servers receive scancodes from keyboard
drivers. A scancode can either be comprised of one
byte or three bytes. In each byte, the most
significant bit (assuming unsigned bytes) is ignore,
however for it first byte in the scancode it
signifies whether the key was released: it is set of
the key is released, and not set if the key was
pressed or is being held down.

A scancode is comprised of three bytes if the lower
7-bits of the first byte is are all cleared, and the
highest bit in the two following bytes are set.

@cpindex Keycodes
Ignoring the most significant bit in all bytes, the
keycode is the value of the byte if the scancode is a
single byte scancode. If the scancode is comprised of
three bytes, the first byte is ignored and the
keycode is @math{a \cdot 128 + b} where @math{a} is
the value of the second byte and @math{b} is the value
of the third byte.

@menu
* 105-keys Keycodes::               List of keycodes for 105-keys keyboards.
@end menu



@node 105-keys Keycodes
@section 105-keys Keycodes

This is a list of keyboards for the 105-keys
keyboards, using QWERTY-layout for reference.

@table @asis
@item @code{1}
@key{Escape} key
@item @code{2}--@code{11}
Keys: @key{1}, @key{2}, @key{3}, @key{4}, @key{5},
@key{6}, @key{7}, @key{8}, @key{9}, @key{0}
@item @code{12}
Key right of @key{0}.
@item @code{13}
Key left of @key{Backspace}
@item @code{14}
@key{Backspace} key
@item @code{15}
@key{Tab} key
@item @code{16}--@code{25}
Keys: @key{q}, @key{w}, @key{e}, @key{r}, @key{t},
@key{y}, @key{u}, @key{i}, @key{o}, @key{p}
@item @code{26}
Key right of @key{p}, once removed
@item @code{27}
Key right of @key{p}, twice removed
@item @code{28}
@key{Return} key
@item @code{29}
Left @key{Control} key
@item @code{30}--@code{38}
Keys: @key{a}, @key{s}, @key{d}, @key{f}, @key{g},
@key{h}, @key{j}, @key{k}, @key{l}
@item @code{39}
Key right of @key{l}, once removed
@item @code{40}
Key right of @key{l}, twice removed
@item @code{41}
Key left of @key{1}
@item @code{42}
Left @key{Shift} key
@item @code{43}
Key right of @key{l}, three times removed
@item @code{44}--@code{50}
Keys: @key{z}, @key{x}, @key{c}, @key{v}, @key{b},
@key{n}, @key{m}
@item @code{51}
Key right of @key{m}, once removed
@item @code{52}
Key right of @key{m}, twice removed
@item @code{53}
Key right of @key{m}, three times removed
@item @code{54}
Right @key{Shift} key
@item @code{55}
@key{Multiply} key on the keypad
@item @code{56}
@key{Alternative} key
@item @code{57}
@key{Space} key
@item @code{58}
@key{Caps Lock} key
@item @code{59}--@code{68}
Keys: @key{F1} through @key{F10}
@item @code{69}
@key{Num Lock} key
@item @code{70}
@key{Scroll Lock} key
@item @code{71}--@code{73}
@key{7}, @key{8}, @key{9} keys on the keypad
@item @code{74}
@key{Minus} key on the keypad
@item @code{75}--@code{77}
@key{4}, @key{5}, @key{6} keys on the keypad
@item @code{78}
@key{Plus} key on the keypad
@item @code{79}--@code{82}
@key{1}, @key{2}, @key{3}, @key{0} keys on the keypad
@item @code{83}
@key{Comma} key on the keypad
@item @code{86}
Key left of @key{z}
@item @code{87}
@key{F11} key
@item @code{88}
@key{F12} key
@item @code{96}
@key{Return} key on the keypad
@item @code{97}
Right @key{control} key
@item @code{98}
@key{Divide} key on the keypad
@item @code{99}
@key{System Request}/@key{Print Screen} key
@item @code{100}
@key{Alternative Graphic} key
@item @code{102}
@key{Home} key
@item @code{103}
@key{Up} arrow key
@item @code{104}
@key{Page up} key
@item @code{105}
@key{Left} arrow key
@item @code{106}
@key{Right} arrow key
@item @code{107}
@key{End} key
@item @code{108}
@key{Down} arrow key
@item @code{109}
@key{Page down} down
@item @code{110}
@key{Insert} key
@item @code{111}
@key{Delete} key
@item @code{119}
@key{Pause}/@key{Break} key
@item @code{125}
Left @key{Super} key
@item @code{126}
Right @key{Super} key
@item @code{127}
@key{Application Menu} key
@end table



@node Keyboard Layouts
@chapter Keyboard Layouts

@cpindex Keyboard layouts, files
@cpindex Keyboard layouts, compile
@cpindex Compiling keyboard layouts
@fnindex @command{mds-kbdc}
Keyboard layouts are compiled from one or more files.
When compiling a layout from multiple files, it is
important that the files are specified in the correct
order. The general rule is that the layout file, for
example the Swedish QWERTY-keyboard, is specified
first and is followed by add-ons such as the compose
table and layout modifiers. @command{mds-kbdc} is
used to compile layouts.

Installed keyboard layout files are located in
@file{/usr/share/mds/keyboard}.@footnote{If you are
hacking in the source tree, you will find this under
@file{res/keyboard}.} Layouts are located in the
subdirectory @file{layout}, modifiers are located in
the subdirectory @file{mods} and compose tables are
located in the subdirectory @file{compose}.
@command{mds-kbdc} prefixes
@file{/usr/share/mds/keyboard} unless the specifed
files starts with @file{/}, @file{./} or @file{../}.
Dead keys are implemented by compose tables and not
in the layouts.

@menu
* Keyboard Layout Syntax::                    How to write your how layouts.
* Builtin Functions::                         Functions provided by the compiler.
@end menu



@node Keyboard Layout Syntax
@section Keyboard Layout Syntax

@cpindex Keyboard layout, files, syntax
@cpindex Syntax of keyboard layout file
Similar to the C programming language, keyboard layout
files are parsed from the top down. This means that
any function or macro can only be used from lines
below the definition of said callable. However, the
order of the mapping statements themself, in respect
to each other, does not matter. Additionally, the
layout files are parsed line by line, and leading
whitespace is ignored. Comment can be started with a
#-character and end at the end of the line. It is
important to know that modifiers like @key{Shift} and
@key{Control} needs to be mapped from a keycode, this
and similar that many keyboards have in common,
except dead key composition and compose sequences, is
already available in the @file{layout/common}
directory and can be included from the layout file.
Compositions are implement in the @file{compose}
directory and should be selected by the user at
compile-time. Keyboard layout files must be written
in UTF-8 (without UTF-8 BOM) and with line feeds for
new lines.

@menu
* Mapping Statements::                        Mapping keycodes to logical keys and text.
* Sequence Mapping::                          Implementing dead keys and compositions.
* Keyboard Layout Identification::            Specifing the layout language, country and variant.
* Layout Assumptions::                        Making assumption about the keyboard layout.
* Include Statement::                         Including base files.
* Layout Macros and Functions::               Reducing repetition.
* Escaping::                                  Backslashes have so many uses.
@end menu



@node Mapping Statements
@subsection Mapping Statements

The most fundamental part of the layout files are
mapping statements. These specify which keycode the
keys have and what happens when certain keys pressed,
combined or pressed and a sequence. If we want to map
keycode 57 to the space key we write

@example
<keycode 57> : <space>
@end example

but then we also want the space key to product a blank
space when we are writting so we add

@example
<space> : " "
@end example

giving us

@example
@group
<keycode 57> : <space>
<space> : " "
@end group
@end example

Because the order of the mapping statements does not
matter we can just as well write

@example
@group
<space> : " "
<keycode 57> : <space>
@end group
@end example

@code{" "} represents a text string with one blank
space, but it is possible to have multiple characters.

If we want to extend this to @kbd{altgr+space}
producing a no-break space, we can add either of the
lines

@example
@group
<altgr space> : "\u00A0" # no-break space (# comment)
<altgr keycode 57> : "\u00A0" # no-break space
@end group
@end example

However, we also need a mapping to @kbd{altgr}:

@example
<keycode 100> : <altgr>
@end example

If we want to add a mapping to @kbd{ultra} from
@kbd{altgr+menu} we can write

@example
@group
<keycode 127> : <menu>
<altgr menu> : <-altgr ultra>
@end group
@end example

@code{-altgr} means that @kbd{altgr} should not be
reported as held down.

@cpindex Lock keys
@cpindex Keys, lock
As can be seen in these examples it is not possible
to distinguish between modifiers and keys. It is up
to the keyboard layout server and keyboard layout
compiler to know this. However, it is defined in the
keyboard layout files whether modifiers keys are lock
keys or not. To map the keycode 58 to @kbd{caps lock}
write

@example
<keycode 58> : <caps lock>
@end example

But if you do not want it be a lock key, but instead
be required to be held down, similar to how is normal
for @key{Shift}, instead write

@example
<keycode 58> : <caps>
@end example

Any modifier may be a lock key.

Another, just as important, use of mappings to is map
letter keys. Unlike @key{Control} keys like
@key{Space} and @key{Shift}, there are no predefined
letters@footnote{With letters with mean any character
other than space.}. Therefore the letter is prefixed
with the word `letter'. For example:

@ifset AFOURPAPER_OR_USLETTER
@example
<keycode 16> : <letter q>     # The Q-key has keycode 16 (on QWERTY)
<letter q> : "q"              # The Q-key should produce a `q'
<shift letter q> : "Q"        # but `Q' when shift is used
<caps q> : "Q"                # or when caps is used
<shift caps letter q> : "q"   # but not when both are used
@end example
@end ifset
@ifclear AFOURPAPER_OR_USLETTER
@example
# The Q-key has keycode 16 (on QWERTY)
<keycode 16> : <letter q>
# The Q-key should produce a `q'
<letter q> : "q"
# but `Q' when shift is used
<shift letter q> : "Q"
# or when caps is used
<caps q> : "Q"
# but not when both are used
<shift caps letter q> : "q"
@end example
@end ifclear

Special characters like simple double quotes,
backspace and, in @code{<>}-notation, greater than
sign must be escaped with a prepending backslash.

@cpindex Dead keys
@cpindex Compose key
@cpindex Modifier keys
@cpindex Keys, dead
@cpindex Keys, compose
@cpindex Keys, modifiers
Many keyboard layouts also have dead keys. Dead keys
are keys that affect the next key-press. For example,
`´' followed by `e' may product `é'. @kbd{compose}
may be a dead key, just like it is in X.org, but it
can also be a modifer.

To define @kbd{´}, with keycode 13, @kbd{compose},
with keycode 125, as a dead keys write

@example
@group
<keycode 13> : <dead letter ´>
<keycode 125> : <dead compose>
@end group
@end example

@cpindex Duplicate keys
@cpindex Keys, duplicates
Some may appear on multiple locations on the keyboard,
for example, there may be a left and a right
@key{Shift} key, and a normal @key{Return} key and
one on the keypad:

@example
<keycode 42> : <left shift>
<keycode 54> : <right shift>
<keycode 28> : <return>
<keycode 96> : <keypad return>
@end example

@cpindex Arrow keys
@cpindex Keys, arrows
Because @code{<left>} and @code{<right>} are valid
keys --- they are arrow keys --- it is important to
place them directly before the key, and not after.
For instance @code{<left shift>} denotes the left
@key{Shift} key, whilst @code{<shift left>} denotes
the @key{Left} arrow key with a @key{Shift} key held
down. Modifiers goes first.



@node Sequence Mapping
@subsection Sequence Mapping

@cpindex Dead keys
@cpindex Compose key
@cpindex Keys, dead
@cpindex Keys, compose
@cpindex Compose tables
@cpindex Key sequences
@cpindex Sequence, keys
Compose tables use mapping statements to map key
sequences. For example the compose key followed by
two `s':es makes an `ß':

@example
<dead compose> "s" "s" : "ß"
@end example

It is also possible to map a sequence to another
sequence:

@example
<dead compose> <tab> : <tab> <tab> <tab> <tab>
@end example

Of course, the input does not need to be
a sequence:

@example
<super tab> : <tab> <tab> <tab> <tab>
@end example

An alternative to @key{Compose} as a dead key, is
@key{Compose} as a modifier. If you use this, the
compose table need to be written for just that. There
two ways do this this. Either you can write for
example

@example
<compose "s"> <compose "s"> : "ß"
@end example

This maps two `s':es to a `ß', but requires that
@key{Compose} is held down during both key-presses.
The other way is to write

@example
<compose "s", "s"> : "ß" # Note the `,'
@end example

This also requires that @kbd{compose} is not
released between the key-presses.

The compose table is filled with compositions where
it does not matter in which order you press some of
the keys. For example, instead of

@example
@group
<dead compose> "S" "|" : "$"
<dead compose> "|" "S" : "$"
@end group
@end example

you can write

@example
<dead compose> ("S" "|") : "$"
@end example

@cpindex Key subsequences, unordered
@cpindex Subsequence, unordered, keys
@cpindex Unordered subsequence, keys
@cpindex Alternation, keys
@cpindex Key alternations
@code{( )} denotes an unordered subsequence. You can
also use @code{[ ]} for alternation. For example,
instead of

@example
@group
<dead compose> ("S" "|") : "$"
<dead compose> ("s" "|") : "$"
@end group
@end example

you can write

@example
<dead compose> (["S" "s"] "|") : "$"
@end example

Inside an alternation you can use a dot for specify
that no key press is needed. For example, instead of

@example
@group
<dead compose> "|" "S" : "$"
<dead compose> "|" "|" "S" : "$"
@end group
@end example

you can write

@example
<dead compose> "|" ["|" .] "S" : "$"
@end example

It is undefined in which order alternations and
unordered subsequences are expanded; neither
sequencewise or levelwise. Thus, there should not be
side-effects where either one is used, nor does it
make since to nest the two constructs in any other
way than alternation or unordered subsequence inside
unordered subsequence. The compiler may however
choose to discourage unordered subsequence inside
unordered subsequence because of readability issues.

Unordered subsequences longer than 5 elements cannot
compile under normal circumstances. Eliminiation of
unordered subsequences grows superexponentially, and
thus is probably an error than can cause memory
exhaustion and unrealistic compilation-time.
Therefore, if an unordered subsequences longer than 5
elements is used the compiler required that the
@option{--force} flag is used and that the unordered
subsequences uses double brackets:

@ifset AFOURPAPER_OR_USLETTER
@example
<dead compose> ("1" "2" "3" "4" "5") : "120"
<dead compose> (("1" "2" "3" "4" "5" "6")) : "720"
<dead compose> (("1" "2" "3" "4" "5" "6" "7")) : "5040"
<dead compose> (("1" "2" "3" "4" "5" "6" "7" "8")) : "40320"
<dead compose> (("1" "2" "3" "4" "5" "6" "7" "8" "9")) : "362880"
@end example
@end ifset
@ifclear AFOURPAPER_OR_USLETTER
@ifset SMALLBOOK_WITH_SMALLFONT
@example
<dead compose> ("1" "2" "3" "4" "5") : "120"
<dead compose> (("1" "2" "3" "4" "5" "6")) : "720"
<dead compose> (("1" "2" "3" "4" "5" "6" "7")) : "5040"
<dead compose> (("1" "2" "3" "4" "5" "6" "7" "8")) : "40320"
@end example
@end ifset
@ifclear SMALLBOOK_WITH_SMALLFONT
@example
@group
<dead compose> ("1" "2" "3" "4" "5") : "120"
<dead compose> (("1" "2" "3" "4" "5" "6")) : "720"
<dead compose> (("1" "2" "3" "4" "5" "6" "7")) : "5040"
@end group
@end example
@end ifclear
@end ifclear



@node Keyboard Layout Identification
@subsection Keyboard Layout Identification

@cpindex Keyboard layout identification
@cpindex Identification of keyboard layouts
Whilst it is possible to write a comment that states
what keyboard layout a file implements, there is a
standardise way to do this in code. The intention with
this is to make it possible for graphical tools to
easily list the layouts and easy to understand
descriptions.

There are three things a keyboard layout file should
specify: the language, the country where it is used,
and the variant.

For example the Swedish QWERTY layout used in Sweden
would have the code.

@example
information
  language "Swedish"
  country "Sweden"
  variant "QWERTY"
end information
@end example

@cpindex Keyboard layout country
@cpindex Keyboard layout language
@cpindex Keyboard layout variant
@cpindex Country, keyboard layout
@cpindex Language, keyboard layout
@cpindex Variant, keyboard layout
If the layout is used multiple countries, or even for
multiple lanuages, @code{country} and @code{language}
may be specified on multiple lines. For example:

@example
information
  language "Spanish"
  country "Argentina"
  country "Bolivia, Plurinational State of"
  country "Chile"
  country "Colombia"
  country "Costa Rica"
  country "Cuba"
  country "Dominican Republic"
  country "Ecuador"
  country "El Salvador"
  country "Guatemala"
  country "Haiti"
  country "Honduras"
  country "Mexico"
  country "Nicaragua"
  country "Panama"
  country "Paraguay"
  country "Peru"
  country "Puerto Rico"
  country "Uruguay"
  country "Venezuela, Bolivarian Republic of"
  variant "Latin American, QWERTY"
end information
@end example

or

@example
information
  language "Norwegian"
  language "Bokmål"
  language "Nynorsk"
  country "Norway"
  variant "QWERTY"
end information
@end example



@node Layout Assumptions
@subsection Layout Assumptions

@cpindex Keyboard layout, file inclusion
@cpindex File inclusion, keyboard layout
@cpindex Inclusion of file, keyboard layout
When writing generic compose tables it can be helpful
to let the compiler assume that a certain set of keys
will be provided by the layout file and not making
other assumptions. This is helpful because if you want
to make an compose table that can compose all
characters given only the ASCII letters, modifiers
and a compose key, rather than written a phony layout
file and select it each time you compile to compose
table you can state in the compose table file that
the compiler should as that those keys are provided
when the compose table file is compile by itself. If
this is done, the compiler can warn when one of the
compositions cannot be reached from those basic keys.

If we want to make the compiler assume that
@key{compose} is available as a dead key, that
@key{shift}, @key{altgr} and @key{space} are
available and that the ASCII letter, digits and some
basic special characters are available we can write.

@example
assumption
  have <dead compose>
  have <shift>
  have <altgr>
  have <space>
  have_range "0" "9"
  have_range "a" "z"
  have_range "A" "Z"
  have_chars "!\"@@#$%&/@{([)]=@}?\\^~*'<>|,;.:-_"
end assumption
@end example



@node Include Statement
@subsection Include Statement

@cpindex Keyboard layout, file inclusion
@cpindex File inclusion, keyboard layout
@cpindex Inclusion of file, keyboard layout
Writing layout files from scratch is probably
something you want to avoid. For instance you would
we need to create mappings for `A' to `Z' and `0' to
`9' (assuming its a latin-based language), and map up
all specific key, like modifiers, space, arrow keys,
and the keypad. And you would have to make sure do
only that the keys are mapped but that they are
mapped to the text the should product and that they
word correcly with the modifiers. These are things
most keyboards have in common with many other layouts.

For instance @file{layout/sv/qwerty} has two include
statements to implement its basics:

@example
@group
include "../common/qwerty"
include "../common/base"
@end group
@end example



@node Layout Macros and Functions
@subsection Layout Macros and Functions

@cpindex Keyboard layout, macros
@cpindex Macros, keyboard layout
There is a lot of repetitive work in layouts, for
instance all letters need mapping for any combination
of use of @key{shift} and @key{compose}. To reduce
this, you can define macros.

For example instead of writing

@example
<letter a> : "a"
<shift letter a> : "A"
<caps letter a> : "A"
<shift caps letter a> : "a"

<letter b> : "b"
<shift letter b> : "B"
<caps letter b> : "B"
<shift caps letter b> : "b"

# and so on ...
@end example

you can use a macro and write

@example
macro letter/2
  <letter \1> : "\1"
  <shift letter \1> : "\2"
  <caps letter \1> : "\2"
  <shift caps letter \1> : "\1"
end macro

letter("a" "A")
letter("b" "B")
# and so on ...
@end example

The name of this macro is @code{letter/2}, but it is
called with the name @code{letter} and two arguments.
The @code{/2}-suffix means that it is invoked with
exactly two arguments. You can use this do define
multiple version of the same macro, with the same
invocation name but with different number of
arguments. For example:

@example
macro letter/2
  <letter \1> : "\1"
  <shift letter \1> : "\2"
  <caps letter \1> : "\2"
  <shift caps letter \1> : "\1"
end macro
macro letter/1
  letter(\1 \add(\sub(\1 "a") "A"))
end macro

letter("a")
letter("b")
# and so on ...
letter("å" "Å")
letter("ä" "Ä")
letter("ö" "Ö")
@end example

@code{\add( )} and @code{\sub( )} are calls to two
built-in functions named @code{add/2} and
@code{sub/2}.

@cpindex Alternation, keys
@cpindex Key alternations
Alternation can be used to invoke a macro:

@ifset AFOURPAPER_OR_USLETTER_OR_SMALLFONT
@example
@group
letter(["a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m"])
letter(["n" "o" "p" "q" "r" "s" "t" "u" "v" "w" "x" "y" "z"])
@end group
@end example
@end ifset
@ifclear AFOURPAPER_OR_USLETTER_OR_SMALLFONT
@example
@group
letter(["a" "b" "c" "d" "e" "f" "g" "h" "i" "j"])
letter(["k" "l" "m" "n" "o" "p" "q" "r" "s" "t"])
letter(["u" "v" "w" "x" "y" "z"])
@end group
@end example
@end ifclear

@cpindex Alternation, keys
@cpindex Key alternations
You may use @code{.} in an alternation, in that case
macro is called once with the argument, causing it to
invoke for example @code{letter/0} instead of
@code{letter/1}.

A related issue are for-loops. If we for example want
to call the macro @code{letter/1} for all letters
between and including `a' and `z' we can just write

@example
@group
for "a" to "z" as \1
  letter(\1)
end for
@end group
@end example

instead of using the alternation-trick.

You call also use if-statments. For example

@example
for "à" to "þ" as \1
  # times sign is not upper case of division sign
  if \not(\equals(\1 "\u00F7"))
    letter(\1 \add(\sub(\1 "à") "À"))
  end if
end for
@end example

or equivalently

@example
for "à" to "þ" as \1
  if \equals(\1 "\u00F7")
    continue # times sign is not upper case of division sign
  end if
  letter(\1 \add(\sub(\1 "à") "À"))
end for
@end example

@code{continue} can be used to stop the iteration of
the innermost for-loop and skip to the next iteration.
You can also use @code{break}, but it also has the
effect to stop the entire loop. Similarly,
@code{return} can be used to break an entire macro
call, or function call.

You can also use @code{if} for more example things,
and use @code{else if} and @code{else if}:

@example
macro latter/1
  if \not(\greater(\1 "z"))
    letter(\1 \add(\sub(\1 "a") "A"))
  else if \not(\greater(\1 "þ"))
    letter(\1 \add(\sub(\1 "à") "À"))
  else
    letter(\1 \sub(\1 1))
  end if
end macro
@end example

Note that there is no quotes around the `a' in
@code{letter(\1 \sub(\1 1))}. This means that the
argument will be than value 1 rather than the code
point of the character `1'. Note however that values
lower than zero or equals to or greater than 2 to the
power of 31 not allowed and can either cause
compile-time error or erroneous compiled files.

@cpindex Keyboard layout, macros
@cpindex Macros, keyboard layout
Functions are similar to function macros, the
difference is that a function is called inline and is
prefixed with slash, and rather than inline the code
inside it, the evalutes to the last value it evaluted
before it returned.

For example instead of @code{\not(\greater(\1 "z"))}
you can write @code{\less_eq(\1 "z")} after you have
defined the function @code{less_eq/2} with the
following code:

@example
@group
function less_eq/2
  \not(\greater(\1 \2))
end function
@end group
@end example

A final construct to make layout code less repetitive
is let-statements. This can be used to assign values
to variables.

The code

@example
macro latter/1
  if \not(\greater(\1 "z"))
    letter(\1 \add(\sub(\1 "a") "A"))
  else if \not(\greater(\1 "þ"))
    letter(\1 \add(\sub(\1 "à") "À"))
  else
    letter(\1 \sub(\1 1))
  end if
end macro
@end example

can equivalently be written using @code{let} as

@example
macro latter/1
  if \not(\greater(\1 "z"))
    let \2 : \sub("a" "A")
  else if \not(\greater(\1 "þ"))
    let \2 : \sub("à" "À")
  else
    let \2 : 1
  end if
  letter(\1 \sub(\1 \2))
end macro
@end example

It is also possible to declare arrays:

@example
let \1 : @{ "å" "ä" "ö" "à" "é" "ü" @}
@end example

Arrays may however not have arrays for values.

Because arrays can be very large, they, but only
them, may span multiple lines. For example you may
write

@example
@group
let \1 : @{
  "å" "ä" "ö" "à" "é" "ü"
  @}
@end group
@end example

but not

@example
@group
let \1 :
  @{ "å" "ä" "ö" "à" "é" "ü" @}
@end group
@end example

See @ref{Builtin Functions} for how they are used.

Variable names can only be numerical and most not
start with a zero. `0' is not valid variable name,
and thus @code{\0} does not address a variable. Macro
and function names, may only include `0'--`9',
`a'--`z', `A'--`Z' and `_', but must and not start
with `0'--`9'. Additionally, when declared macro and
function names must be suffixed with `/' follwed by
the exact number of arguments the macro or function
takes.

Variable indices are constrained to the 31:th power
of 2, exclusively. Attempts to use higher variable
indices invoke undefined behaviour. Additionally
there is no guarantee that the compiler allocates
indexwise spares variables efficiently.

Like variables, the size of arrays are also
restricted to the 31:th power of 2.



@node Escaping
@subsection Escaping

@cpindex Keyboard layout, Escaping special character
@cpindex Keyboard layout, special character, escaping
@cpindex Escaping special character, keyboard layout
@cpindex Special character, escaping, keyboard layout
Similar to most, if not all, programming language, a
backslash inside quotes can be used to parse the next
character with special meaning. For instance, `\"' is
parsed as a literal `"', and `\\' is parsed as a
literal `\'. `\>' is too parsed as a literal `>', for
example you may need to write @code{<letter \>>}. The
characters `(', `)', `[', `]', `@{', `@}', `<' and
`,' also follow this rule to make those character
accesible inside a @code{< >}. But `\' can also be
used to specify characters by their code point, for
example if you want an `æ' you can write
@code{"\u00E6"} or @code{"\uE6"}, instead of
@code{"æ"}. You can also write @code{"\0346"}, the
difference between @code{\0} and @code{\u} is that
@code{\0} uses octal whereas @code{\u} uses
hexadecimal. A noteworthy side-effect of this is that
function names cannot start with a lower case `u'.

`\' can also be used to access variables and
parameters. For example @code{\1} in

@example
macro letter/2
  <letter \1> : "\1"
  <shift letter \1> : "\2"
  <caps letter \1> : "\2"
  <shift caps letter \1> : "\1"
end macro
letter("å" "Å")
@end example

is expanded to an `å', where as @code{\2} is expanded
to an `Å'.

`\' is also used to call functions, for example if
you want to call the function @code{f/0} you write
@code{\f()}.

Because numerical (possibly prefixed with an `u') are
of variable length, it is possible to specify the
escape's termination point with a dot. For instance,
if you want the value of the first variable
(@code{\1}) followed by two zeroes, you do not write
@code{\100} as that would expand to the value of the
hundredth variable. Instead you write @code{\1.00}.

Use of function calls and variables inside
@code{include}-statments invokes undefined behaviour.
Escaped numerals greater than or equal to the 31th
power of 2 also invoke undefined behaviour.


@node Builtin Functions
@section Builtin Functions

@cpindex Keyboard layout, functions, builtin
@cpindex Keyboard layout, builtin functions
@cpindex Functions, builtin, keyboard layout
@cpindex Builtin functions, keyboard layout
To help you write meaningful functions in your
keyboard layout files, the compiler defines an almost
minimal set of basic functions:

@table @code
@item add/2
@fnindex @code{add/2}
The code points in @code{\1} plus the code points
of the corresponding characters in @code{\2}. If
@code{\1} and @code{\2} are not of the same length,
the returned string will be of the length of the
longer of the parameters, and modulo is used to map
to the corresponing character.
@item sub/2
@fnindex @code{sub/2}
Like @code{add/2} but subtraction.
@item mul/2
@fnindex @code{mul/2}
Like @code{add/2} but multiplication.
@item div/2
@fnindex @code{div/2}
Like @code{add/2} but division.
@item mod/2
@fnindex @code{mod/2}
Like @code{add/2} but modulo.
@item rsh/2
@fnindex @code{rsh/2}
Like @code{add/2} but rightward bitwise shift. If a
character in @code{\2} is has a code point greater
than 30, undefined behaviour is invoked.
@item lsh/2
@fnindex @code{lsh/2}
Like @code{add/2} but leftward bitwise shift. If a
character in @code{\2} is has a code point greater
than 30, undefined behaviour is invoked.
@item or/2
@fnindex @code{or/2}
Like @code{add/2} but bitwise OR@.
@item and/2
@fnindex @code{and/2}
Like @code{add/2} but bitwise AND@.
@item xor/2
@fnindex @code{xor/2}
Like @code{add/2} but bitwise XOR@.
@item not/1
@fnindex @code{not/1}
For each character in @code{\1}, evaluate to zero if
the character is not zero, and one if the character
is zero.
@item equals/2
@fnindex @code{equals/2}
For each character, evalute to one if the characters
in @code{\1} and @code{\2} are equal and zero
otherwise.
@item greater/2
@fnindex @code{greater/2}
Like @code{equals/2} but @code{\1} greater than
@code{\2} rather than @code{\1} equals
@code{\2}.
@item less/2
@fnindex @code{less/2}
Like @code{equals/2} but @code{\1} less than
@code{\2} rather than @code{\1} equals @code{\2}.
@item set/3
@fnindex @code{set/3}
Set the element with index @code{\2}, in the array
with variable index @code{\1}, to @code{\3}, and
return @code{\3}. For example @code{\set(1 0 4)} sets
the first element in @code{\1} to 4.
@item get/2
@fnindex @code{get/2}
Return the element with index @code{\2} in the array
with variable index @code{\1}. For example after
@code{\set(1 0 4)} or @code{let \1 : @{ 4 3 2 1 0 @}}
has been used, @code{\get(1 0)} evaluates to 4.
@end table



@node Default Keyboard Layouts
@chapter Default Keyboard Layouts

@cpindex Compose tables
The chapter is about the special keyboard layouts
and compose tables included with @command{mds}.

@menu
* Dead Compose Table::                        The compose table for the dead compose key.
@end menu



@node Dead Compose Table
@section Dead Compose Table

@cpindex Dead keys
@cpindex Compose key
@cpindex Keys, dead
@cpindex Keys, compose
This section describes the structure for the mappings
used in the compose table for the dead key version of
the compose key.

@menu
@c * Aegean Numbers::                            Aegean Numbers.
@c * Alchemical Symbols::                        Alchemical Symbols.
@c * Alphabetic Presentation Forms::             Alphabetic Presentation Forms.
@c * Ancient Greek Musical Notation::            Ancient Greek Musical Notation.
@c * Ancient Greek Numbers::                     Ancient Greek Numbers.
@c * Ancient Symbols::                           Ancient Symbols.
@c * Arabic::                                    Arabic.
@c * Arabic Extended-A::                         Arabic Extended-A@.
@c * Arabic Mathematical Alphabetic Symbols::    Arabic Mathematical Alphabetic Symbols.
@c * Arabic Presentation Forms-A::               Arabic Presentation Forms-A@.
@c * Arabic Presentation Forms-B::               Arabic Presentation Forms-B@.
@c * Arabic Supplement::                         Arabic Supplement.
@c * Armenian::                                  Armenian.
* Arrows::                                    Arrows.
@c * Avestan::                                   Avestan.
@c * Balinese::                                  Balinese.
@c * Bamum::                                     Bamum.
@c * Bamum Supplement::                          Bamum Supplement.
* Basic Latin::                               Basic Latin.
@c * Bassa Vah::                                 Bassa Vah.
@c * Batak::                                     Batak.
@c * Bengali::                                   Bengali.
* Block Elements::                            Block Elements.
@c * Bopomofo::                                  Bopomofo.
@c * Bopomofo Extended::                         Bopomofo Extended.
* Box Drawing::                               Box Drawing.
* Braille Patterns::                          Braille Patterns.
@c * Brahmi::                                    Brahmi.
@c * Buginese::                                  Buginese.
@c * Buhid::                                     Buhid.
@c * Byzantine Musical Symbols::                 Byzantine Musical Symbols.
@c * C0 Controls::                               C0 Controls.
@c * C1 Controls::                               C1 Controls.
@c * Carian::                                    Carian.
@c * Caucasian Albanian::                        Caucasian Albanian.
@c * Chakma::                                    Chakma.
@c * Cham::                                      Cham.
@c * Cherokee::                                  Cherokee.
@c * CJK Compatibility::                         CJK Compatibility.
@c * CJK Compatibility Forms::                   CJK Compatibility Forms.
@c * CJK Compatibility Ideographs::              CJK Compatibility Ideographs.
@c * CJK Compatibility Ideographs Supplement::   CJK Compatibility Ideographs Supplement.
@c * CJK Radicals Supplement::                   CJK Radicals Supplement.
@c * CJK Strokes::                               CJK Strokes.
@c * CJK Symbols and Punctuation::               CJK Symbols and Punctuation.
@c * CJK Unified Ideographs::                    CJK Unified Ideographs.
@c * CJK Unified Ideographs Extension A::        CJK Unified Ideographs Extension A@.
@c * CJK Unified Ideographs Extension B::        CJK Unified Ideographs Extension B@.
@c * CJK Unified Ideographs Extension C::        CJK Unified Ideographs Extension C@.
@c * CJK Unified Ideographs Extension D::        CJK Unified Ideographs Extension D@.
@c * Combining Diacritical Marks::               Combining Diacritical Marks.
@c * Combining Diacritical Marks Extended::      Combining Diacritical Marks Extended.
@c * Combining Diacritical Marks for Symbols::   Combining Diacritical Marks for Symbols.
@c * Combining Diacritical Marks Supplement::    Combining Diacritical Marks Supplement.
@c * Combining Half Marks::                      Combining Half Marks.
@c * Common Indic Number Forms::                 Common Indic Number Forms.
@c * Control Pictures::                          Control Pictures.
@c * Coptic::                                    Coptic.
@c * Coptic Epact Numbers::                      Coptic Epact Numbers.
@c * Counting Rod Numerals::                     Counting Rod Numerals.
@c * Cuneiform::                                 Cuneiform.
@c * Cuneiform Numbers and Punctuation::         Cuneiform Numbers and Punctuation.
@c * Currency Symbols::                          Currency Symbols.
@c * Cypriot Syllabary::                         Cypriot Syllabary.
@c * Cyrillic::                                  Cyrillic.
@c * Cyrillic Extended-A::                       Cyrillic Extended-A@.
@c * Cyrillic Extended-B::                       Cyrillic Extended-B@.
@c * Cyrillic Supplement::                       Cyrillic Supplement.
@c * Deseret::                                   Deseret.
@c * Devanagari::                                Devanagari.
@c * Devanagari Extended::                       Devanagari Extended.
@c * Dingbats::                                  Dingbats.
* Domino Tiles::                              Domino Tiles.
@c * Duployan::                                  Duployan.
@c * Egyptian Hieroglyphs::                      Egyptian Hieroglyphs.
@c * Elbasan::                                   Elbasan.
@c * Emoticons::                                 Emoticons.
* Enclosed Alphanumeric Supplement::          Enclosed Alphanumeric Supplement.
@c * Enclosed Ideographic Supplement::           Enclosed Ideographic Supplement.
* Enclosed Alphanumerics::                    Enclosed Alphanumerics.
@c * Enclosed CJK Letters and Months::           Enclosed CJK Letters and Months.
@c * Ethiopic::                                  Ethiopic.
@c * Ethiopic Extended::                         Ethiopic Extended.
@c * Ethiopic Extended-A::                       Ethiopic Extended-A@.
@c * Ethiopic Supplement::                       Ethiopic Supplement.
* General Punctuation::                       General Punctuation.
* Geometric Shapes::                          Geometric Shapes.
* Geometric Shapes Extended::                 Geometric Shapes Extended.
@c * Georgian::                                  Georgian.
@c * Georgian Supplement::                       Georgian Supplement.
@c * Glagolitic::                                Glagolitic.
@c * Gothic::                                    Gothic.
@c * Grantha::                                   Grantha.
@c * Greek and Coptic::                          Greek and Coptic.
@c * Greek Extended::                            Greek Extended.
@c * Gujarati::                                  Gujarati.
@c * Gurmukhi::                                  Gurmukhi.
@c * Halfwidth and Fullwidth Forms::             Halfwidth and Fullwidth Forms.
@c * Hangul Compatibility Jamo::                 Hangul Compatibility Jamo.
@c * Hangul Jamo::                               Hangul Jamo.
@c * Hangul Jamo Extended-A::                    Hangul Jamo Extended-A@.
@c * Hangul Jamo Extended-B::                    Hangul Jamo Extended-B@.
@c * Hangul Syllables::                          Hangul Syllables.
@c * Hanunoo::                                   Hanunoo.
@c * Hebrew::                                    Hebrew.
@c * Hiragana::                                  Hiragana.
@c * Ideographic Description Characters::        Ideographic Description Characters.
@c * Imperial Aramaic::                          Imperial Aramaic.
@c * Inscriptional Parthian::                    Inscriptional Parthian.
@c * Inscriptional Pahlavi::                     Inscriptional Pahlavi.
* IPA Extensions::                            IPA Extensions.
@c * Javanese::                                  Javanese.
@c * Kaithi::                                    Kaithi.
@c * Kana Supplement::                           Kana Supplement.
@c * Kangxi Radicals::                           Kangxi Radicals.
@c * Kannada::                                   Kannada.
@c * Katakana::                                  Katakana.
@c * Katakana Phonetic Extensions::              Katakana Phonetic Extensions.
@c * Kanbun::                                    Kanbun.
@c * Kayah Li::                                  Kayah Li.
@c * Kharoshthi::                                Kharoshthi.
@c * Khmer::                                     Khmer.
@c * Khmer Symbols::                             Khmer Symbols.
@c * Khojki::                                    Khojki.
@c * Khudawadi::                                 Khudawadi.
@c * Lao::                                       Lao.
@c * Latin Extended Additional::                 Latin Extended Additional.
* Latin Extended-A::                          Latin Extended-A@.
* Latin Extended-B::                          Latin Extended-B@.
* Latin Extended-C::                          Latin Extended-C@.
@c * Latin Extended-D::                          Latin Extended-D@.
@c * Latin Extended-E::                          Latin Extended-E@.
* Latin-1 Supplement::                        Latin-1 Supplement.
@c * Lepcha::                                    Lepcha.
@c * Letterlike Symbols::                        Letterlike Symbols.
@c * Limbu::                                     Limbu.
@c * Linear A::                                  Linear A@.
@c * Linear B Ideograms::                        Linear B Ideograms.
@c * Linear B Syllabary::                        Linear B Syllabary.
@c * Lisu::                                      Lisu.
@c * Lycian::                                    Lycian.
@c * Lydian::                                    Lydian.
@c * Mahajani::                                  Mahajani.
* Mahjong Tiles::                             Mahjong Tiles.
@c * Malayalam::                                 Malayalam.
@c * Mandaic::                                   Mandaic.
@c * Manichaean::                                Manichaean.
@c * Mathematical Alphanumeric Symbols::         Mathematical Alphanumeric Symbols.
* Mathematical Operators::                    Mathematical Operators.
@c * Meetei Mayek::                              Meetei Mayek.
@c * Meetei Mayek Extensions::                   Meetei Mayek Extensions.
@c * Mende Kikakui::                             Mende Kikakui.
@c * Meroitic Cursive::                          Meroitic Cursive.
@c * Meroitic Hieroglyphs::                      Meroitic Hieroglyphs.
@c * Miao::                                      Miao.
* Miscellaneous Mathematical Symbols-A::      Miscellaneous Mathematical Symbols-A@.
* Miscellaneous Mathematical Symbols-B::      Miscellaneous Mathematical Symbols-B@.
@c * Miscellaneous Symbols::                     Miscellaneous Symbols.
* Miscellaneous Symbols and Arrows::          Miscellaneous Symbols and Arrows.
@c * Miscellaneous Symbols and Pictographs::     Miscellaneous Symbols and Pictographs.
@c * Miscellaneous Technical::                   Miscellaneous Technical.
@c * Modi::                                      Modi.
@c * Modifier Tone Letters::                     Modifier Tone Letters.
@c * Mongolian::                                 Mongolian.
@c * Mro::                                       Mro.
@c * Musical Symbols::                           Musical Symbols.
@c * Myanmar::                                   Myanmar.
@c * Myanmar Extended-A::                        Myanmar Extended-A@.
@c * Myanmar Extended-B::                        Myanmar Extended-B@.
@c * Nabataean::                                 Nabataean.
@c * New Tai Lue::                               New Tai Lue.
@c * NKo::                                       NKo.
* Number Forms::                              Number Forms.
@c * Ogham::                                     Ogham.
@c * Ol Chiki::                                  Ol Chiki.
@c * Old North Arabian::                         Old North Arabian.
@c * Old Italic::                                Old Italic.
@c * Old Permic::                                Old Permic.
@c * Old Persian::                               Old Persian.
@c * Old South Arabian::                         Old South Arabian.
@c * Old Turkic::                                Old Turkic.
@c * Optical Character Recognition::             Optical Character Recognition.
@c * Osmanya::                                   Osmanya.
@c * Ornamental Dingbats::                       Ornamental Dingbats.
@c * Oriya::                                     Oriya.
@c * Palmyrene::                                 Palmyrene.
@c * Pahawh Hmong::                              Pahawh Hmong.
@c * Pau Cin Hau::                               Pau Cin Hau.
@c * Phaistos Disc::                             Phaistos Disc.
@c * Phags-pa::                                  Phags-pa.
@c * Phoenician::                                Phoenician.
@c * Phonetic Extensions::                       Phonetic Extensions.
@c * Phonetic Extensions Supplement::            Phonetic Extensions Supplement.
* Playing Cards::                             Playing Cards.
@c * Psalter Pahlavi::                           Psalter Pahlavi.
@c * Rejang::                                    Rejang.
@c * Rumi Numeral Symbols::                      Rumi Numeral Symbols.
@c * Runic::                                     Runic.
@c * Samaritan::                                 Samaritan.
@c * Saurashtra::                                Saurashtra.
@c * Sharada::                                   Sharada.
@c * Shavian::                                   Shavian.
@c * Shorthand Format Controls::                 Shorthand Format Controls.
@c * Siddham::                                   Siddham.
@c * Sinhala::                                   Sinhala.
@c * Sinhala Archaic Numbers::                   Sinhala Archaic Numbers.
@c * Small Form Variants::                       Small Form Variants.
@c * Sora Sompeng::                              Sora Sompeng.
@c * Spacing Modifier Letters::                  Spacing Modifier Letters.
@c * Specials::                                  Specials.
@c * Sundanese::                                 Sundanese.
@c * Sundanese Supplement::                      Sundanese Supplement.
* Superscripts and Subscripts::               Superscripts and Subscripts.
* Supplemental Arrows-A::                     Supplemental Arrows-A@.
* Supplemental Arrows-B::                     Supplemental Arrows-B@.
* Supplemental Arrows-C::                     Supplemental Arrows-C@.
* Supplemental Mathematical Operators::       Supplemental Mathematical Operators.
@c * Syloti Nagri::                              Syloti Nagri.
@c * Syriac::                                    Syriac.
* Tags::                                      Tags.
@c * Tagalog::                                   Tagalog.
@c * Tagbanwa::                                  Tagbanwa.
@c * Tamil::                                     Tamil.
@c * Tai Le::                                    Tai Le.
@c * Tai Tham::                                  Tai Tham.
@c * Tai Viet::                                  Tai Viet.
@c * Tai Xuan Jing Symbols::                     Tai Xuan Jing Symbols.
@c * Takri::                                     Takri.
@c * Telugu::                                    Telugu.
@c * Thaana::                                    Thaana.
@c * Thai::                                      Thai.
@c * Tibetan::                                   Tibetan.
@c * Tifinagh::                                  Tifinagh.
@c * Tirhuta::                                   Tirhuta.
@c * Transport and Map Symbols::                 Transport and Map Symbols.
@c * Unified Canadian Aboriginal Syllabics::     Unified Canadian Aboriginal Syllabics.
@c * Unified Canadian Aboriginal Syllabics Extended:: Unified Canadian Aboriginal Syllabics Extended.
@c * Ugaritic::                                  Ugaritic.
@c * Vai::                                       Vai.
* Variation Selectors::                       Variation Selectors and Variation Selectors Supplement.
@c * Vertical Forms::                            Vertical Forms.
@c * Vedic Extensions::                          Vedic Extensions.
@c * Warang Citi::                               Warang Citi.
@c * Yi Radicals::                               Yi Radicals.
@c * Yi Syllables::                              Yi Syllables.
@c * Yijing Hexagram Symbols::                   Yijing Hexagram Symbols.
@end menu



@node Arrows
@subsection Arrows
@ubindex Arrows

970



@node Basic Latin
@subsection Basic Latin
@ubindex Basic Latin
@ubindex Latin, Basic

125



@node Block Elements
@subsection Block Elements
@ubindex Block Elements

1648



@node Box Drawing
@subsection Box Drawing
@ubindex Box Drawing

Most of the box drawing glyphs can be composed by
typing @kbd{<dead compose>} followed by two glyphs
that should be combined to form the desired glyphs.
If the two glyphs are identical the glyph becomes
heavy. More general, common parts of the glyphs
become heavy.

Glyphs that contain a heavy part be transformed so
that the heavy parts become double stroked. Glyphs
that do not contain heavy parts be transformed so the
entire glyphs becomes double stroked. This is done by
typing @kbd{<dead compose>} followed by, in any
order, @kbd{"+"} and the glyph to modify. Note that
this is not possible for all glyphs, as not all
glyphs have a double stroked variant, but all double
stroked glyphs can be composed this way.

The horizontal and the vertical light glyphs, as well
as the combination of the two, can be made double
stroked by typing @kbd{<dead compose>} followed by,
in any order, @kbd{"="} and the glyph.

The light corners can be made rounded by by typing
@kbd{<dead compose>} followed by, in any order,
@kbd{"o"} and the glyph or @kbd{"O"} and the glyph.

The sequences @kbd{<dead compose> "-" "|"} and
@kbd{<dead compose> "|" "-"} can be used to create
a light horizontal line crossed with a light vertical
line.

Basic box drawing glyphs are created with sequences
starting either with @kbd{<shift dead compose> "b"}
or @kbd{<shift dead compose> "B"}. The former creates
light glyphs, and the latter creates heavy glyphs.
Note that glyphs with diagonal lines do not have an
heavy variants. The base sequences are followed by a
sequence describing the glyphs to compose.
@table @kbd
@item "-"
Horizontal line.
@item "|"
Vertical line.
@item "+"
Horizontal line combined with vertical line.
@item "/"
Diagonal upper right to lower left.
@item "\"
Diagonal upper left to lower right.
@item "X"
Diagonal cross.
@item "<"
Left part of a horizontal line.
@item "^"
Upper part of a vertical line.
@item ">"
Right part of a horizontal line.
@item "v"
Lower part of a vertical line.
@end table
Simple arrows can be used instead of @kbd{"<"},
@kbd{"^"}, @kbd{">"} and @kbd{"v"}.

@kbd{"-"}, @kbd{"|"} can be prefixed with a key to
modify the lines.
@table @kbd
@item "="
Double stroke. This modifier is also available for
@kbd{"+"}.
@item "."
Triple dash.
@item ":"
Quadruple dash.
@end table

Double dashed horizonal line is composed with
@kbd{<shift dead compose> "b" "." "."} for the light
variant and @kbd{<shift dead compose> "B" "." "."}
for the heavy. variant. @kbd{"." ":"}, or a broken
pipe, instead of @kbd{"." "."} can be used to create
a double dashed vertical line.



@node Braille Patterns
@subsection Braille Patterns
@ubindex Braille Patterns

The sequence @kbd{<shift dead compose> "b" <space>}
can be used to create a blank braille pattern.

A single-dot braille pattern can be composed with
@kbd{<shift dead compose> "b"} followed by a digit
key between @kbd{"1"} and @kbd{"8"}, representing
the index of the dot.

A dual-dot braille pattern can be composed with
@kbd{<shift dead compose> "B"} followed by two digit
keys between @kbd{"1"} and @kbd{"8"}, representing
the indices of the dots.

More complex braille patterns are composed by
overlaying two braille patterns. This is done by
typing @kbd{<dead compose>} followed by the two
braille patterns to overlay. If the two braille
patterns are identical, the braille pattern will be
overlays with its mirror pattern.



@node Domino Tiles
@subsection Domino Tiles
@ubindex Domino Tiles
@c TODO compose tiles together

There are two types of domino tile glyphs:
horizontal and vertical. Each tile has two halfs with
0 to 6 dots. Additonally there is one horizontal
tile, and one vertical tile, with the back facing the
user.

Horizontal tiles are composed with
@kbd{<shift dead compose> "d" "t" "-"} followed by
the number of dots on the left side and the number of
dots on the right side. Horizontal tile with the back
facing the user is composed with either @kbd{"-"} or
@kbd{<space>} instead of the two digits.

Vertical tiles are composed with
@kbd{<shift dead compose> "d" "t" "|"} followed by
the number of dots on the top and the number of dots
on the bottom. Vertical tile with the back facing
the user is composed with either @kbd{"|"} or
@kbd{<space>} instead of the two digits.



@node Enclosed Alphanumeric Supplement
@subsection Enclosed Alphanumeric Supplement
@ubindex Enclosed Alphanumeric Supplement

1476



@node Enclosed Alphanumerics
@subsection Enclosed Alphanumerics
@ubindex Enclosed Alphanumerics

3133



@node General Punctuation
@subsection General Punctuation
@ubindex General Punctuation
@ubindex Punctuation, General

730



@node Geometric Shapes
@subsection Geometric Shapes
@ubindex Geometric Shapes

1687



@node Geometric Shapes Extended
@subsection Geometric Shapes Extended
@ubindex Geometric Shapes Extended

3194



@node IPA Extensions
@subsection IPA Extensions
@ubindex IPA Extensions

568



@node Latin Extended-A
@subsection Latin Extended-A
@ubindex Latin Extended-A

236



@node Latin Extended-B
@subsection Latin Extended-B
@ubindex Latin Extended-B

364



@node Latin Extended-C
@subsection Latin Extended-C
@ubindex Latin Extended-C

2834



@node Latin-1 Supplement
@subsection Latin-1 Supplement
@ubindex Latin-1 Supplement

136



@node Mahjong Tiles
@subsection Mahjong Tiles
@ubindex Mahjong Tiles

Unnumbered mahjong tiles are composed with
@kbd{<shift dead compose> "m" "t"} followed by one
additional key:
@table @kbd
@item <
West tile
@item v
South tile
@item >
East tile
@item ^
North tile
@item r
Red dragon tile
@item g
Green dragon tile
@item w
White dragon tile
@item m
Plum (mei) tile
@item l
Orchid (lan) tile
@item z
Bamboo (zhu) tile
@item j
Chrysanthemum (ju) tile
@item 1
Spring tile
@item 2
Summer tile
@item 3
Autumn tile
@item 4
Winter tile
@item *
Joker tile
@item /
The back of a mahjong tile
@end table

The numbered tiles are composed with
@kbd{<shift dead compose> "m" "t"} followed by with
additional keys: one for the suit, and one for the
value. The value is is encoded with either @kbd{"1"}
to @kbd{"9"}. The suits is encoded
@table @kbd
@item W
Characters (wan)
@item T
Bamboos (tiao)
@item B
Circles (bing)
@end table



@node Mathematical Operators
@subsection Mathematical Operators
@ubindex Mathematical Operators

1118



@node Miscellaneous Mathematical Symbols-A
@subsection Miscellaneous Mathematical Symbols-A
@ubindex Miscellaneous Mathematical Symbols-A
@ubindex Mathematical Symbols-A, Miscellaneous

1824



@node Miscellaneous Mathematical Symbols-B
@subsection Miscellaneous Mathematical Symbols-B
@ubindex Miscellaneous Mathematical Symbols-B
@ubindex Mathematical Symbols-B, Miscellaneous

2119



@node Miscellaneous Symbols and Arrows
@subsection Miscellaneous Symbols and Arrows
@ubindex Miscellaneous Symbols and Arrows
@ubindex Symbols and Arrows, Miscellaneous
@ubindex Arrows, Miscellaneous Symbols and

2594



@node Number Forms
@subsection Number Forms
@ubindex Number Forms

889



@node Playing Cards
@subsection Playing Cards
@ubindex Playing Cards

@kbd{<shift dead compose> "p" "c"} composes the
character presenting the back of a playing card.

Jokers and trumps are composed using the playing card
back and two additional characters.

@table @asis
@item joker, red
@kbd{<dead compose> <playing card back> "j" "r"}
@item joker, white
@kbd{<dead compose> <playing card back> "j" "w"}
@item joker, black
@kbd{<dead compose> <playing card back> "j" "b"}
@end table

The red joker can be composed with the sequence
@kbd{<dead compose> <shift dead compose> "p" "c" "j" "r"},
becuase @kbd{<playing card back>} can be composed with
the sequence @kbd{<shift dead compose> "p" "c"}.

The trumps are number 1 through 21, and are composed
with @kbd{<dead compose> <playing card back> "1" <space>}
through @kbd{<dead compose> <playing card back> "2" "1"}.
Additionally, the fool card is composed with through
@kbd{<dead compose> <playing card back> "0" <space>}.

The Playing Cards block in Unicode also contains ace,
2--10, jack, knight, queen och king for the suits
spades/swords, hearts/cups, diamonds/pentacles and
clubs/wands. These are composed with the
@kbd{<dead compose>} followed by, in any order, the
suit and value. The values are encoded
@table @asis
@item Ace
@kbd{"A"}, @kbd{"a"} or @kbd{"1"}
@item 2--9
@kbd{"2"} through @kbd{"9"}
@item 10
@kbd{"0"}
@item Jack
@kbd{"J"} or @kbd{"j"}
@item Knight
@kbd{"C"} or @kbd{"c"}
@item Queen
@kbd{"Q"} or @kbd{"q"}
@item King
@kbd{"K"} or @kbd{"k"}
@end table
and the suits are encoded
@table @asis
@item Spades or Swords
Black or white spades symbol
@item Hearts or Cups
Black or white hearts symbol
@item Diamonds or Pentacles
Black or white diamonds symbol
@item Clubs or Wands
Black or white clubs symbol
@end table



@node Superscripts and Subscripts
@subsection Superscripts and Subscripts
@ubindex Superscripts and Subscripts
@ubindex Subscripts, Superscripts and

840



@node Supplemental Arrows-A
@subsection Supplemental Arrows-A
@ubindex Supplemental Arrows-A
@ubindex Arrows-A, Supplemental

1900



@node Supplemental Arrows-B
@subsection Supplemental Arrows-B
@ubindex Supplemental Arrows-B
@ubindex Arrows-B, Supplemental

1973



@node Supplemental Arrows-C
@subsection Supplemental Arrows-C
@ubindex Supplemental Arrows-C
@ubindex Arrows-C, Supplemental

3284



@node Supplemental Mathematical Operators
@subsection Supplemental Mathematical Operators
@ubindex Supplemental Mathematical Operators
@ubindex Mathematical Operators, Supplemental

2286



@node Tags
@subsection Tags
@ubindex Tags

The ``Tags'' block in Unicode has been deprecated.
Characters in this block is therefore not mapped in
the compose table.



@node Variation Selectors
@subsection Variation Selectors
@ubindex Variation Selectors
@ubindex Variation Selectors Supplement
@c TODO Variation Selectors, Variation Selectors Supplement

There are 256 variation selectors, numbered 1 through
256. These can be composed with the sequence
@kbd{<shift dead compose> "v" "s"} followed by
exactly three digits. These digits should form the
index of the variation selector. Indices lower than
100, require leading @kbd{"0"}:s. Alternatively,
variation selectors with an index lower than 100,
can be composed with a trailing @kbd{<space>} instead
of leading @kbd{"0"}:s.



@node Accessibility
@chapter Accessibility

@menu
* Sticky Keys::                               Ephemeral key-locking.
* Bounce Keys::                               Key repetition-elimination.
* Slow Keys::                                 Key press-acceptance delay.
* Loud Keys::                                 Keyboard tiggered sound cues.
* Mouse Keys::                                Controlling the mouse with the keyboard.
@end menu
@c TODO vector grapics compatible magnifier



@node Sticky Keys
@section Sticky Keys

@pgindex @command{mds-keystick}
@cpindex Sticky keys
@cpindex Keyboard, accessibility
@cpindex Accessibility, keyboard
Sticky keys is an accessibility feature that lets the
user process modifier keys instead of holding them
down. Sticky keys is implemented by the
@command{mds-keystick} server.

When @command{mds-keystick} is active, any key that
is mapped in @command{mds-keystick} to be a modifier
is held down once press and not released until an
non-modifier is released. It is possible for map any
key to have this feature, that do not have to be
actual modifiers, that is, modifiers according to
@command{mds-keytrans}.

If a key is press three times without any intermediate
keys, and is a modifier, that key released until it is
pressed again.

Note that @command{mds-keystick} is not aware of which
keys are considered modifiers by
@command{mds-keytrans}, but it is affected of
remappings in @command{mds-kbd} and
@command{mds-kkbd}, therefore it is better to swap,
for example, @kbd{control} and @kbd{caps lock} in the
keyboard servers than in @command{mds-keytrans}. Doing
so means that you do not have to configure
@command{mds-keystick} to know the original
@kbd{caps lock} is a modifier but the original
@kbd{control} is not.

@cpindex Mode lock key
@cpindex Keys, mode lock
For greater accessibility you can, in
@command{mds-keytrans}, replace a key with the
@kbd{mode lock}-key. If this is done, pressing a
sequence of modifiers and then the @kbd{mode lock}-key
will caused those modifiers to be locked until the
next time you press @kbd{mode lock}. Any modifier
pressed directly before, optionally with intermediate
modifiers, the second @kbd{mode lock} will stay
locked. The action of @kbd{mode lock} is to release
all modifiers it is locked and the lock those that
are currently held down; active stickly keys are
artificially held down and thus included.



@node Bounce Keys
@section Bounce Keys

@pgindex @command{mds-keybounce}
@cpindex Bounce keys
@cpindex Keyboard, accessibility
@cpindex Accessibility, keyboard
Bounce keys is an accessibility feature that filters
out rapidly repeated key strokes. Bounce keys is
implemented by the @command{mds-keybounce} server.



@node Slow Keys
@section Slow Keys

@pgindex @command{mds-slowkey}
@cpindex Slow keys
@cpindex Keyboard, accessibility
@cpindex Accessibility, keyboard
Slow keys is an accessibility feature that filters out
brief key strokes. Slow keys is implemented by the
@command{mds-slowkey} server.



@node Loud Keys
@section Loud Keys

@pgindex @command{mds-keycue}
@cpindex Loud keys
@cpindex Keyboard, accessibility
@cpindex Accessibility, keyboard
Loud keys is an accessibility feature that can emulate
key clicking sounds when a key is pressed or generate
tones when certain keys are pressed. For example if
@kbd{caps lock} is actived by a key stroke a
high-pitched tone can be generated when when it is
deactived by a key stroke a low-pitched tone can be
generated. Loud keys is implemented by the
@command{mds-keycue} server.



@node Mouse Keys
@section Mouse Keys

@pgindex @command{mds-kbd2rat}
@cpindex Keyboard to rat bindings
@cpindex Rat keys
@cpindex Mouse keys
Rat keys (also known as mouse keys) is an
accessibility and usability feature that lets the
user use the keyboard as a pointing device. This
feature is implemented by the @command{mds-kbd2rat}
server, and this section covers the details of that
server.

If @command{mds-kbd2rat} is used, the keypad acts as a
pointing device when @kbd{num lock} is not active. It
is also possible to configure @command{mds-kbd2rat} to
disregard @kbd{num lock} and always be active, until
it receives a signal to toggle its state. For example,
if @command{mds-kbd2rat} is configured to disregard
@kbd{num lock}, @command{mds-kbdtrans} can be
configured to send to fauxkey @kbd{rat} when
@kbd{alt+shift+num} is pressed, and this key can be
caught by @command{mds-keybind} that sends a signal to
@command{mds-kbd2rat} to toggle.

When @command{mds-kbd2rat} is active, it maps the
keypad to the rat according to the following table:

@table @kbd
@item division
Right-hand left (primary) rat button.

@item multiplication
Middle (modifier) rat button.

@item subtraction
Right-hand (alternate) right rat button.

@item addition
Scroll up.

@item return
Scroll down.

@item comma
Cancel actions waiting by @kbd{0} and
@kbd{5}.

@item 0
Hold down the next selected rat button until that rat
button is selected again. This is a dead key, that
is, you do not have to hold it down.

@item 1
Cursor left down.

@item 2
Cursor down.

@item 3
Cursor right down.

@item 4
Cursor left.

@item 5
Double click with the next selected
rat button. This is a dead key, that is,
you do not have to hold it down.
If pressed twice, a triple click triggered
instead, and so on. If this key is prefixed
by @kbd{0}, the last click will be replaced
by hold down action.

@item 6
Cursor right.

@item 7
Cursor left up.

@item 8
Cursor up.

@item 9
Cursor right up.
@end table

This table is not affected by mappings in
@command{mds-keytrans}, but it is affected by
remappings in @command{mds-kbd} and
@command{mds-kkbd}.

@command{mds-kbd2rat} can be configured to permute
the rat button keys. It is independent of
permutations in @command{mds-rat}.

If multiple direction keys@footnote{@kbd{1}, @kbd{2},
@kbd{3}, @kbd{3}, @kbd{4}, @kbd{6}, @kbd{7}, @kbd{8}
and @kbd{9}} are used, the average direction is used.

@command{mds-kbd2rat} is five parameters that control
with which speed it moves the cursor:

@table @asis
@item delay
The delay it takes before the first time a mouse
event is repeated when a key is held down. The
default is for the server to wait for the keyboard to
send another key press.

@item interval
The time it takes before a mouse event is repeated
since its previous repear when a key is held down.
The default is for the server to wait for the
keyboard to send another key press.

@item max speed
The maximum speed with which the cursor can move.

@item time to max speed
The time a key has to be held down before the maximum
speed is reached. The cursor accelerate with each
mouse event repeat.

@item curve
Ramp used to reach pointer speed.
@end table

The pointer's speed, not taking caps into
consideration, is calculated by

@iftex
@math{max~speed \left ( hold~down~time ~-~ delay \over time~to~max~speed \right)^{1 ~+~ curve}}
@end iftex
@ifnottex
max speed ((hold down time - delay) / time to max
speed)^(1 + curve)
@end ifnottex



@node Specifications
@chapter Specifications

@menu
* Rat Cursors::                               Rat cursor specifications.
* Nesting Applications::                      Specifications for nesting applications.
* The Real Display Server::                   Identifying the real display server.
@end menu



@node Rat Cursors
@section Rat Cursors

@cpindex Cursor, specifications
@cpindex Rat cursor, specifications
@cpindex Mouse cursor, specifications
@pgindex @command{mds-cursorshadow}
@cpindex Cursor shadow
@cpindex Rat cursor shadow
@cpindex Mouse cursor shadow
@cpindex Shadow, cursor
Rat cursor themes should not add shadows to the
cursors. Shadows are added by the
@command{mds-cursorshadow} server according to the
user's specifications.

@command{mds}'s rat cursors specifications are based on
@url{http://www.freedesktop.org/wiki/Specifications/cursor-spec}.

All rat cursor themes should include the cursors
listed below. The icons are conceptual examples of
how they can look.

@cpindex Cursor animation
@cpindex Rat cursor animation
@cpindex Mouse cursor animation
@cpindex Animation, cursors
In addition to the cursors below, each of the may be
accompanied with @code{X-press}, @code{X-hold} and
@code{X-release}, where @code{X} is the name of the
master icon. @code{X-press} is an animation from
@code{X} to @code{X-hold} and is used when the cursor
should transition from @code{X} to @code{X-hold}.
@code{X-hold} is the version of @code{X} that should
be used if any rat button is held down. @code{X} is
an animation from @code{X-release} to @code{X} and is
used when the cursor should transition from
@code{X-release} to @code{X}@. Clients should not set
the cursor to either of them, it is up to the server
to do this based on events from the rat device.

@ifset AFIVEPAPER
@page
@end ifset
@table @code
@item default
This is the default cursor. It is used as a fallback
if no more fitting cursor is found; for example if a
programs wants the cursor to be @command{pointer},
but the server is unable to find it, it will fallback
to @command{default}. The server should provide its
own fallback in case the theme is missing this cursor
too.

This cursor indicates that the interface is idle and
prepared to accept commands from the user.

This cursor is usually a north-west- or
north-north-west-pointing arrow. For left-handed
themes this cursor is usually a north-east- or
north-north-east-pointing arrow.
@example
@group
##
####
######
########
##########
############
##############
################
##################
############
######  ####
####    ######
##        ####
          ######
            ####
            ####
@end group
@end example

@page
@item context-menu
@cpindex Menus, context menus
@cpindex Context menus
This cursor indicates the same state as
@command{default} with he addition that the object
beneath it can be right-clicked (left-clicked if
left-handed) to open a context menu.

This cursor is typically @command{default} combined
with a small menu.
@example
@group
##                  ############
####                ############
######              ##        ##
########            ############
##########          ##        ##
############        ############
##############      ##        ##
################    ############
##################
############
######  ####
####    ######
##        ####
          ######
            ####
            ####
@end group
@end example
@vskip 0pt plus 1filll

@ifset AFIVEPAPER
@page
@end ifset
@item text
@cpindex Text, horizontal
@cpindex Horizontal text
This cursor should be used when the rat pointers is
above an horizontal text that can be selected and
possibly edited.

This cursor is usually a vertical I-beam.
@example
@group
##############
      ##
      ##
      ##
      ##
      ##
      ##
      ##
      ##
      ##
      ##
      ##
      ##
      ##
      ##
##############
@end group
@end example
@vskip 0pt plus 1filll

@ifclear AFOURPAPER_WITH_SMALLFONT
@page
@end ifclear
@item vertical-text
@cpindex Text, vertical
@cpindex Vertical text
@cpindex Text, rotated
@cpindex Rotated text
This cursor should be used when the rat pointers is
above an vertical text that can be selected and
possibly edited.

If this cursor is missing, @code{text} should be used
as the first fallback.

This cursor is usually a horizontal I-beam.
@example
@group
##                            ##
##                            ##
##                            ##
################################
##                            ##
##                            ##
##                            ##
@end group
@end example
@vskip 0pt plus 1filll

@ifset AFOURPAPER_WITH_SMALLFONT
@page
@end ifset
@item progress
@cpindex Wait cursor
@cpindex Progress cursor
This cursor indicates that the interface can be used
as when @command{default} is used. But that the
program is working in the background with command the
user previously issued.

This cursor is usually rendered as a combination of
@command{default} and @command{wait}.
@example
@group
##                  ############
####                ############
######                ########
########                ####
##########              ####
############          ########
##############      ############
################    ############
##################
############
######  ####
####    ######
##        ####
          ######
            ####
            ####
@end group
@end example
@vskip 0pt plus 1filll

@ifclear AFOURPAPER_WITH_SMALLFONT
@page
@end ifclear
@item wait
@cpindex Wait cursor
@cpindex Progress cursor
This cursor indicates that the interface cannot be
used because it is working or is blocked by an
external resource.

This cursor is typically rendered as a hourglass,
watch, sundial or some sort of animated ring.
@example
@group
      ####################
      ####################
        ################
          ############
            ########
              ####
              ####
              ####
              ####
              ####
              ####
            ########
          ############
        ################
      ####################
      ####################
@end group
@end example
@vskip 0pt plus 1filll

@ifset AFIVEPAPER_OR_AFOURPAPER_WITH_SMALLFONT
@page
@end ifset
@item pointer
@cpindex Clickable
@cpindex Links
This cursor indicates that the object beneath it is
clickable. Typically a link in a Web browser.
However, it should not be used for pushbuttons and
other user interface elements where it is apparent by
design that the object is clickable.

This cursor is usually a right hand (left hand if
left-handed) pointing with the index-finger.
@example
@group
        ####
        ####
        ####
        ####
        ####  ####
        ####  ####  ####
  ##    ####  ####  ####  ####
######  ################  ####
  ##############################
    ############################
      ##########################
      ##########################
        ########################
        ########################
          ####################
            ################
@end group
@end example
@vskip 0pt plus 1filll

@ifclear AFOURPAPER_WITH_SMALLFONT
@page
@end ifclear
@item help
@cpindex Help mode
This cursor indicates that the interface is in
context help mode. This is usually activated by
clicking an help button --- which usally has a
question mark on it --- on the titlebar.

This cursor is typically renderas as @code{default}
with a question mark next to it.
@example
@group
##                ######
####            ##########
######        ####      ####
########                ####
##########            ####
############        ####
##############      ####
################    ####
##################
############        ####
######  ####        ####
####    ######
##        ####
          ######
            ####
            ####
@end group
@end example
@vskip 0pt plus 1filll

@item drag
@cpindex Drag-and-drop
This cursor indicates that an object is being dragged.

This cursor is usually a closed right hand, or closed
left hand if left-handed.
@example
@group
    ####  ####  ####
    ################  ####
############################
############################
############################
  ##########################
    ########################
    ########################
      ####################
        ################
@end group
@end example
@vskip 0pt plus 1filll

@page
@item copy
@cpindex Drag-and-drop, copy
@cpindex Copy, drag-and-drop
This cursor indicates that the dragged object will be
copied or listed upon release.

If this cursor is missing, @code{drag} should be used
as the first fallback.

This cursor is usually rendered as @code{drag} with a
plus-sign next to it.
@example
@group
                          ##
                          ##
                      ##########
                          ##
                          ##
 
    ####  ####  ####
    ################  ####
############################
############################
############################
  ##########################
    ########################
    ########################
      ####################
        ################
@end group
@end example
@vskip 0pt plus 1filll

@ifset AFIVEPAPER
@page
@end ifset
@item move
@cpindex Drag-and-drop, move
@cpindex Move, drag-and-drop
This cursor indicates that the dragged object will be
moved upon release, or otherwise acted upon.

If this cursor is missing, @code{drag} should be used
as the first fallback.

This cursor is usually rendered as @code{drag} with
an arrow next to it. The arrow is usually point
north-east, or north-west if left-handed.
@example
@group
                      ######
                      ####
                      ##  ##
                            ##
                              ##

    ####  ####  ####
    ################  ####
############################
############################
############################
  ##########################
    ########################
    ########################
      ####################
        ################
@end group
@end example
@vskip 0pt plus 1filll

@page
@item alias
@cpindex Drag-and-drop, link
@cpindex Link, drag-and-drop
@cpindex Drag-and-drop, alias
@cpindex Alias, drag-and-drop
This cursor indicates that the dragged object will be
aliased upon release, or otherwise acted upon. This
may entail creating a symlink.

If this cursor is missing, @code{drag} should be used
as the first fallback.

This cursor is usually rendered as @code{drag} with
an two or three linked links next to it, or an arced
arrow.
@example
@group
                  ####    ####
                ##            ##
                ##  ########  ##
                ##            ##
                  ####    ####
 
    ####  ####  ####
    ################  ####
############################
############################
############################
  ##########################
    ########################
    ########################
      ####################
        ################
@end group
@end example
@vskip 0pt plus 1filll

@ifclear AFOURPAPER
@ifclear SMALLBOOK_WITH_SMALLFONT
@ifclear USLETTER_WITH_SMALLFONT
@page
@end ifclear
@end ifclear
@end ifclear
@item no-drop
@cpindex Drag-and-drop
This cursor indicates that the dragged object cannot
be release where the rat pointer is located, but that
the object beneath it usually allow drops of objects
with similar class to the dragged object.

If this cursor is missing, @code{not-allowed} should
be used as the first fallback, and @code{drag} should
be used as the second fallback.

This cursor is typically rendered as a combination of
@code{drag} and @code{not-allowed}.
@example
@group
                      ########
                    ##      ####
                    ##    ##  ##
                    ##  ##    ##
                    ####      ##
                      ########
    ####  ####  ####
    ################  ####
############################
############################
############################
  ##########################
    ########################
    ########################
      ####################
        ################
@end group
@end example
@vskip 0pt plus 1filll

@page
@item not-allowed
@cpindex Invalid
@cpindex Not allowed
This cursor indicates that the region beneath the rat
pointer is invalid for the current operation.

This cursor is often rendered as a circle with a
diagonal line through it.
@example
@group
            ########
        ####        ####
      ##                ##
    ##                  ####
  ##                  ##    ##
  ##                ##      ##
##                ##          ##
##              ##            ##
##            ##              ##
##          ##                ##
  ##      ##                ##
  ##    ##                  ##
    ####                  ##
      ##                ##
        ####        ####
            ########
@end group
@end example
@vskip 0pt plus 1filll

@ifset AFIVEPAPER
@page
@end ifset
@item all-scroll
@cpindex Scrolling
This cursor is used to indicate that moving the rat
will also move the object beneath below the cursor

This cursor is often rendered as a combined vertical
and horizontal twin-headed arrow.
@example
@group
              ##
            ######
          ##########
              ##
              ##
    ##        ##        ##
  ####        ##        ####
##############################
  ####        ##        ####
    ##        ##        ##
              ##
              ##
          ##########
            ######
              ##
@end group
@end example
@vskip 0pt plus 1filll

@ifclear AFIVEPAPER_OR_AFOURPAPER_WITH_SMALLFONT
@page
@end ifclear
@item up-arrow
@cpindex Insertion point
This cursor is typically used to identify an
insertion point.

It is often rendered an upwards-pointing arrow.
@example
@group
      ##
    ######
  ##########
##############
    ######
    ######
    ######
    ######
    ######
    ######
    ######
@end group
@end example
@vskip 0pt plus 1filll

@ifset AFOURPAPER_WITH_SMALLFONT
@page
@end ifset
@item cell
@cpindex Spread-sheets
@cpindex Cell selection
@cpindex Tables, selection
This cursor is often used in spread-sheet applications
when selecting cells.

It is typically rendered as a thick plus-sign.
@example
@group
          ######
          ######
          ######
          ######
          ######
##########################
##########################
##########################
          ######
          ######
          ######
          ######
          ######
@end group
@end example
@vskip 0pt plus 1filll

@ifclear AFOURPAPER_WITH_SMALLFONT
@page
@end ifclear
@item col-resize
@cpindex Tables, resize
@cpindex Columns, resize
@cpindex Resize table columns
This cursor is used to indicate the the cursor is
within a region that allows it rat to be used to
resize a column.

If this cursor is missing, @code{ew-resize} should
be used as the first fallback, and @code{ew-select}
should be used as the second fallback.

This cursor is typically rendered as a vertical bar
with an arrow from the left side pointing horizontally
towards it and an arrow from the right side pointing
horizontally towards it.
@example
@group
              ##
              ##
              ##
              ##
              ##
      ##      ##      ##
      ####    ##    ####
############  ##  ############
      ####    ##    ####
      ##      ##      ##
              ##
              ##
              ##
              ##
              ##
@end group
@end example
@vskip 0pt plus 1filll

@ifclear AFOURPAPER
@ifclear USLETTER_WITH_SMALLFONT
@page
@end ifclear
@end ifclear
@ifset AFOURPAPER_WITH_SMALLFONT
@page
@end ifset
@item row-resize
@cpindex Tables, resize
@cpindex Rows, resize
@cpindex Resize table rows
This cursor is used to indicate the the cursor is
within a region that allows it rat to be used to
resize a column.

If this cursor is missing, @code{ns-resize} should be
used as the first fallback, and @code{ns-select}
should be used as the second fallback.

This cursor is typically rendered as a horizontal bar
with an arrow from the left side pointing vertically
towards it and an arrow from the right side pointing
vertically towards it.
@example
@group
              ##
              ##
              ##
          ##########
            ######
              ##

##############################

              ##
            ######
          ##########
              ##
              ##
              ##
@end group
@end example
@vskip 0pt plus 1filll

@ifclear USLETTER
@ifclear SMALLBOOK_WITH_SMALLFONT
@ifclear AFOURPAPER_WITH_SMALLFONT
@page
@end ifclear
@end ifclear
@end ifclear
@ifset USLETTER_WITH_SMALLFONT
@page
@end ifset
@item crosshair
@cpindex Drawing
@cpindex Precision drawing
@cpindex Crosshair cursor
This cursor is used for precision drawing or
precision manipulation of an area.

This cursor typically a thin crosshair.
@example
@group
              ##
              ##
              ##
              ##
              ##
              ##
              ##
##############################
              ##
              ##
              ##
              ##
              ##
              ##
              ##
@end group
@end example
@vskip 0pt plus 1filll

@item w-resize
@cpindex Resizing
@cpindex Window resizing
If this cursor is missing, @code{w-select} should be
used as the first fallback, @code{ew-resize} should
be used as the second fallback, @code{ew-select}
should be used as the third fallback, and
@code{col-resize}. should be used as the fourth
fallback.

This cursor is typically rendered as a west-pointing
arrow, optionally with a wall at the arrowhead.
@example
@group
##        ##
##      ##
##    ##
##  ############################
##    ##
##      ##
##        ##
@end group
@end example
@vskip 0pt plus 1filll

@ifset AFOURPAPER_WITH_SMALLFONT
@page
@end ifset
@item w-select
@cpindex Cell selection
@cpindex Tables, selection
If this cursor is missing, @code{w-resize} should be
used as the first fallback, @code{ew-select} should
be used as the second fallback, @code{ew-resize}
should be used as the third fallback, and
@code{col-resize}. should be used as the fourth
fallback.

This cursor is typically rendered as a west-pointing
arrow.
@example
@group
      ##
    ##
  ##
############################
  ##
    ##
      ##
@end group
@end example
@vskip 0pt plus 1filll

@ifclear AFIVEPAPER_OR_USLETTER_OR_SMALLBOOK_WITH_SMALLFONT
@ifclear AFOURPAPER_WITH_SMALLFONT
@page
@end ifclear
@end ifclear
@ifset USLETTER_WITH_SMALLFONT
@page
@end ifset
@item e-resize
@cpindex Resizing
@cpindex Window resizing
If this cursor is missing, @code{e-select} should be
used as the first fallback, @code{ew-resize} should
be used as the second fallback, @code{ew-select}
should be used as the third fallback, and
@code{col-resize}. should be used as the fourth
fallback.

This cursor is typically rendered as a east-pointing
arrow, optionally with a wall at the arrowhead.
@example
@group
                    ##        ##
                      ##      ##
                        ##    ##
############################  ##
                        ##    ##
                      ##      ##
                    ##        ##
@end group
@end example
@vskip 0pt plus 1filll

@ifset AFIVEPAPER_OR_USLETTER_OR_SMALLBOOK_WITH_SMALLFONT
@ifclear USLETTER_WITH_SMALLFONT
@page
@end ifclear
@end ifset
@item e-select
@cpindex Cell selection
@cpindex Tables, selection
If this cursor is missing, @code{e-resize} should be
used as the first fallback, @code{ew-select} should
be used as the second fallback, @code{ew-resize}
should be used as the third fallback, and
@code{col-resize}. should be used as the fourth
fallback.

This cursor is typically rendered as a east-pointing
arrow.
@example
@group
                    ##
                      ##
                        ##
############################
                        ##
                      ##
                    ##
@end group
@end example
@vskip 0pt plus 1filll

@ifset SMALLBOOK
@ifclear SMALLFONT
@page
@end ifclear
@end ifset
@ifset AFOURPAPER_WITH_SMALLFONT
@page
@end ifset
@item n-resize
@cpindex Resizing
@cpindex Window resizing
If this cursor is missing, @code{n-select} should be
used as the first fallback, @code{ns-resize} should
be used as the second fallback, @code{ns-select}
should be used as the third fallback, and
@code{row-resize}. should be used as the fourth
fallback.

This cursor is typically rendered as a north-pointing
arrow, optionally with a wall at the arrowhead.
@example
@group
##############

      ##
    ######
  ##  ##  ##
##    ##    ##
      ##
      ##
      ##
      ##
      ##
      ##
      ##
      ##
      ##
      ##
@end group
@end example
@vskip 0pt plus 1filll

@ifclear SMALLBOOK
@ifclear AFOURPAPER_WITH_SMALLFONT
@page
@end ifclear
@end ifclear
@ifset SMALLBOOK_WITH_SMALLFONT
@page
@end ifset
@item n-select
@cpindex Cell selection
@cpindex Tables, selection
If this cursor is missing, @code{n-resize} should be
used as the first fallback, @code{ns-select} should
be used as the second fallback, @code{ns-resize}
should be used as the third fallback, and
@code{row-resize}. should be used as the fourth
fallback.

This cursor is typically rendered as a north-pointing
arrow.
@example
@group
      ##
    ######
  ##  ##  ##
##    ##    ##
      ##
      ##
      ##
      ##
      ##
      ##
      ##
      ##
      ##
      ##
@end group
@end example
@vskip 0pt plus 1filll

@ifclear AFOURPAPER_OR_USLETTER_OR_SMALLBOOK_WITH_SMALLFONT
@page
@end ifclear
@ifset AFOURPAPER_WITH_SMALLFONT
@page
@end ifset
@item s-resize
@cpindex Resizing
@cpindex Window resizing
If this cursor is missing, @code{s-select} should be
used as the first fallback, @code{ns-resize} should
be used as the second fallback, @code{ns-select}
should be used as the third fallback, and
@code{row-resize}. should be used as the fourth
fallback.

This cursor is typically rendered as a south-pointing
arrow, optionally with a wall at the arrowhead.
@example
@group
      ##
      ##
      ##
      ##
      ##
      ##
      ##
      ##
      ##
      ##
##    ##    ##
  ##  ##  ##
    ######
      ##

##############
@end group
@end example
@vskip 0pt plus 1filll

@ifclear SMALLBOOK
@ifclear AFOURPAPER_WITH_SMALLFONT
@page
@end ifclear
@end ifclear
@item s-select
@cpindex Cell selection
@cpindex Tables, selection
If this cursor is missing, @code{s-resize} should be
used as the first fallback, @code{ns-select} should
be used as the second fallback, @code{ns-resize}
should be used as the third fallback, and
@code{row-resize}. should be used as the fourth
fallback.

This cursor is typically rendered as a south-pointing
arrow.
@example
@group
      ##
      ##
      ##
      ##
      ##
      ##
      ##
      ##
      ##
      ##
##    ##    ##
  ##  ##  ##
    ######
      ##
@end group
@end example
@vskip 0pt plus 1filll

@ifset AFIVEPAPER_OR_AFOURPAPER_WITH_SMALLFONT
@page
@end ifset
@item nw-resize
@cpindex Resizing
@cpindex Window resizing
If this cursor is missing, @code{nw-select}
should be used as the first fallback,
@code{nwse-resize} should be used as the second
fallback, @code{nwse-select} should be used as the
third fallback, and @code{all-resize}. should be used
as the fourth fallback.

This cursor is typically rendered as a
north-west-pointing arrow, optionally with a corner
at the arrowhead.
@example
@group
##################
##
##
##    ############
##    ####
##    ##  ##
##    ##    ##
##    ##      ##
##    ##        ##
                  ##
                    ##
                      ##
                        ##
                          ##
                            ##
                              ##
@end group
@end example
@vskip 0pt plus 1filll

@ifclear SMALLBOOK
@ifclear AFOURPAPER_WITH_SMALLFONT
@page
@end ifclear
@end ifclear
@item nw-select
@cpindex Cell selection
@cpindex Tables, selection
If this cursor is missing, @code{nw-resize} should be
used as the first fallback, @code{nwse-select} should
be used as the second fallback, @code{nwse-resize}
should be used as the third fallback, and
@code{all-resize}. should be used as the fourth
fallback.

This cursor is typically rendered as a
north-west-pointing arrow.
@example
@group
############
####
##  ##
##    ##
##      ##
##        ##
            ##
              ##
                ##
                  ##
                    ##
                      ##
                        ##
@end group
@end example
@vskip 0pt plus 1filll

@ifset AFIVEPAPER_OR_AFOURPAPER_WITH_SMALLFONT
@page
@end ifset
@item se-resize
@cpindex Resizing
@cpindex Window resizing
If this cursor is missing, @code{se-select} should be
used as the first fallback, @code{nwse-resize} should
be used as the second fallback, @code{nwse-select}
should be used as the third fallback, and
@code{all-resize}. should be used as the fourth
fallback.

This cursor is typically rendered as a
south-east-pointing arrow, optionally with a corner
at the arrowhead.
@example
@group
##
  ##
    ##
      ##
        ##
          ##
            ##
              ##        ##    ##
                ##      ##    ##
                  ##    ##    ##
                    ##  ##    ##
                      ####    ##
              ############    ##
                              ##
                              ##
              ##################
@end group
@end example
@vskip 0pt plus 1filll

@ifclear SMALLBOOK
@ifclear AFOURPAPER_WITH_SMALLFONT
@page
@end ifclear
@end ifclear
@item se-select
@cpindex Cell selection
@cpindex Tables, selection
If this cursor is missing, @code{se-resize} should be
used as the first fallback, @code{nwse-select} should
be used as the second fallback, @code{nwse-resize}
should be used as the third fallback, and
@code{all-resize}. should be used as the fourth
fallback.

This cursor is typically rendered as a
south-east-pointing arrow.
@example
@group
##
  ##
    ##
      ##
        ##
          ##
            ##
              ##        ##
                ##      ##
                  ##    ##
                    ##  ##
                      ####
              ############
@end group
@end example
@vskip 0pt plus 1filll

@ifset AFIVEPAPER_OR_AFOURPAPER_WITH_SMALLFONT
@page
@end ifset
@item ne-resize
@cpindex Resizing
@cpindex Window resizing
If this cursor is missing, @code{ne-select} should be
used as the first fallback, @code{nesw-resize} should
be used as the second fallback, @code{nesw-select}
should be used as the third fallback, and
@code{all-resize}. should be used as the fourth
fallback.

This cursor is typically rendered as a
north-east-pointing arrow, optionally with a corner
at the arrowhead.
@example
@group
              ##################
                              ##
                              ##
              ############    ##
                      ####    ##
                    ##  ##    ##
                  ##    ##    ##
                ##      ##    ##
              ##        ##    ##
            ##
          ##
        ##
      ##
    ##
  ##
##
@end group
@end example
@vskip 0pt plus 1filll

@ifclear SMALLBOOK
@ifclear AFOURPAPER_WITH_SMALLFONT
@page
@end ifclear
@end ifclear
@item ne-select
@cpindex Cell selection
@cpindex Tables, selection
If this cursor is missing, @code{ne-resize} should be
used as the first fallback, @code{nesw-select} should
be used as the second fallback, @code{nesw-resize}
should be used as the third fallback, and
@code{all-resize}. should be used as the fourth
fallback.

This cursor is typically rendered as a
north-east-pointing arrow.
@example
@group
              ############
                      ####
                    ##  ##
                  ##    ##
                ##      ##
              ##        ##
            ##
          ##
        ##
      ##
    ##
  ##
##
@end group
@end example
@vskip 0pt plus 1filll

@ifset AFIVEPAPER_OR_AFOURPAPER_WITH_SMALLFONT
@page
@end ifset
@item sw-resize
@cpindex Resizing
@cpindex Window resizing
If this cursor is missing, @code{sw-select} should be
used as the first fallback, @code{nesw-resize} should
be used as the second fallback, @code{nesw-select}
should be used as the third fallback, and
@code{all-resize}. should be used as the fourth
fallback.

This cursor is typically rendered as a
south-west-pointing arrow, optionally with a corner
at the arrowhead.
@example
@group
                              ##
                            ##
                          ##
                        ##
                      ##
                    ##
                  ##
##    ##        ##
##    ##      ##
##    ##    ##
##    ##  ##
##    ####
##    ############
##
##
##################
@end group
@end example
@vskip 0pt plus 1filll

@ifclear SMALLBOOK
@ifclear AFOURPAPER_WITH_SMALLFONT
@page
@end ifclear
@end ifclear
@item sw-select
@cpindex Cell selection
@cpindex Tables, selection
If this cursor is missing, @code{sw-resize} should be
used as the first fallback, @code{nesw-select} should
be used as the second fallback, @code{nesw-resize}
should be used as the third fallback, and
@code{all-resize}. should be used as the fourth
fallback.

This cursor is typically rendered as a
south-west-pointing arrow.
@example
@group
                        ##
                      ##
                    ##
                  ##
                ##
              ##
            ##
##        ##
##      ##
##    ##
##  ##
####
############
@end group
@end example
@vskip 0pt plus 1filll

@item ew-resize
@cpindex Resizing
@cpindex Window resizing
If this cursor is missing, @code{ew-select} should be
used as the first fallback, and @code{col-resize}.
should be used as the second fallback.

This cursor is typically rendered as an east- and
west-pointing twin-arrow, optionally with a wall at
the arrowheads.
@example
@group
##        ##        ##        ##
##      ##            ##      ##
##    ##                ##    ##
##  ########################  ##
##    ##                ##    ##
##      ##            ##      ##
##        ##        ##        ##
@end group
@end example
@vskip 0pt plus 1filll

@ifset SMALLFONT
@ifset AFOURPAPER_OR_AFIVEPAPER
@page
@end ifset
@end ifset
@item ew-select
@cpindex Cell selection
@cpindex Tables, selection
If this cursor is missing, @code{ew-resize} should be
used as the first fallback, and @code{col-resize}.
should be used as the second fallback.

This cursor is typically rendered as an east- and
west-pointing twin-arrow.
@example
@group
      ##        ##
    ##            ##
  ##                ##
########################
  ##                ##
    ##            ##
      ##        ##
@end group
@end example
@vskip 0pt plus 1filll

@ifclear AFIVEPAPER_OR_AFOURPAPER_WITH_SMALLFONT
@page
@end ifclear
@item ns-resize
@cpindex Resizing
@cpindex Window resizing
If this cursor is missing, @code{ns-select} should be
used as the first fallback, and @code{row-resize}.
should be used as the second fallback.

This cursor is typically rendered as a north- and
south-pointing twin-arrow, optionally with a wall at
the arrowheads.
@example
@group
##############

      ##
    ######
  ##  ##  ##
##    ##    ##
      ##
      ##
      ##
      ##
##    ##    ##
  ##  ##  ##
    ######
      ##

##############
@end group
@end example
@vskip 0pt plus 1filll

@item ns-select
@cpindex Cell selection
@cpindex Tables, selection
If this cursor is missing, @code{ns-resize} should be
used as the first fallback, and @code{row-resize}.
should be used as the second fallback.

This cursor is typically rendered as a north- and
south-pointing twin-arrow.
@example
@group
      ##
    ######
  ##  ##  ##
##    ##    ##
      ##
      ##
      ##
      ##
##    ##    ##
  ##  ##  ##
    ######
      ##
@end group
@end example
@vskip 0pt plus 1filll

@ifclear SMALLFONT
@ifclear AFIVEPAPER
@page
@end ifclear
@end ifclear
@ifset USLETTER_WITH_SMALLFONT
@page
@end ifset
@ifset AFOURPAPER_WITH_SMALLFONT
@page
@end ifset
@item nwse-resize
@cpindex Resizing
@cpindex Window resizing
If this cursor is missing, @code{all-resize} should
be used as the first fallback.

This cursor is typically rendered as a north-west- and
south-east-pointing twin-arrow, optionally with a
corner at the arrowheads.
@example
@group
##################
##
##
##    ############
##    ####
##    ##  ##
##    ##    ##
##    ##      ##        ##    ##
##    ##        ##      ##    ##
                  ##    ##    ##
                    ##  ##    ##
                      ####    ##
              ############    ##
                              ##
                              ##
              ##################
@end group
@end example
@vskip 0pt plus 1filll

@ifset AFIVEPAPER
@page
@end ifset
@item nesw-resize
@cpindex Resizing
@cpindex Window resizing
If this cursor is missing, @code{all-resize} should
be used as the first fallback.

This cursor is typically rendered as a north-east- and
south-west-pointing twin-arrow, optionally with a
corner at the arrowheads.
@example
@group
              ##################
                              ##
                              ##
              ############    ##
                      ####    ##
                    ##  ##    ##
                  ##    ##    ##
##    ##        ##      ##    ##
##    ##      ##        ##    ##
##    ##    ##
##    ##  ##
##    ####
##    ############
##
##
##################
@end group
@end example
@vskip 0pt plus 1filll

@page
@item all-resize
@cpindex Resizing
@cpindex Window resizing
This cursor is typically rendered as a cross between
a north-east and south-west-pointing twin-arrow and a
north-west- and south-east-pointing twin-arrow,
optionally with a corner at the arrow heads.
@example
@group
##########          ##########
####                      ####
##  ##                  ##  ##
##    ##              ##    ##
##      ##          ##      ##
          ##      ##
            ##  ##
              ##
            ##  ##
          ##      ##
##      ##          ##      ##
##    ##              ##    ##
##  ##                  ##  ##
####                      ####
##########          ##########
@end group
@end example
@end table

@cpindex Cell selection
@cpindex Tables, selection
In addition, it is advised to @code{nwse-select} and
@code{nesw-select} that are rendered in the same mannar
as the other @code{*-select} cursors and analogously to
@code{nwse-resize} and @code{nesw-resize},
respectively.

@cpindex Text, rotated
@cpindex Rotated text
It is also advisd to a cursors intermediate to
@code{text} and @code{vertical-text}. These are named
with the pattern @code{text-*}, where @code{*} is
replaced by the number of degrees the text is rotated
anti-clockwise. This means that @code{text} should be
used if @code{text-0} is requested but missing, and
@code{vertical-text} should be used if @code{text-90}
is requested but missing. Finally, the closest
existing cursor should be used, and the cursor rotated
180 degrees of what is requested should be used if
there is no matching cursor with a rotation distance
within, but excluding, 90 degrees. @code{*} should be
in the interval [0; 360[, and a period (`.') should be
used as a decimal pointer, as it is used in most
programming languages.



@node Nesting Applications
@section Nesting Applications

@cpindex Nesting applications
@cpindex Applications, nesting
@cpindex Embedding applications
@cpindex Applications, embedding
@vrindex @env{MDS_EMBED}
Applications that want to embed another other
application within it, should create a socket and
start the other application with the environment
variable @env{MDS_EMBED} set to the windows ID of the
socket that the application should be embedded in.

All @command{mds} applications must be aware of the
environment variable @env{MDS_EMBED}@. The
application may choose not to embed itself in the
announced socket, however it should have good reason
for not doing this.

All @command{mds} application must unset the
environment variable @env{MDS_EMBED} before it starts
any other program.

@comment TODO
@c How do we solve this for compatibility with X, Wayland and Mir?



@node The Real Display Server
@section The Real Display Server

@cpindex Real display server
@cpindex Actual display server
@cpindex Preferred display server
@cpindex Display server, real
@cpindex Display server, actual
@cpindex Display server, preferred
@cpindex Compatibility layers
@vrindex @env{PREFERRED_DISPLAY}
The environment variable @env{PREFERRED_DISPLAY},
should be set with the value @code{mds}, if and only
if @command{mds} is started as a display server and
not as a compatibility layer.

@env{PREFERRED_DISPLAY} is a space-separated (U+0020)
list of supported display server protocol, ordered by
preference. 

If @command{mds} is started as a compatibility layer,
@code{mds} should be added to @env{PREFERRED_DISPLAY}
if and only if @env{PREFERRED_DISPLAY} lists any
other display protocol.

If a compatibility server is successfully started, it
shoul be listed in @env{PREFERRED_DISPLAY}@. Be sure
to keep the list ordered by preference.

@table @code
@item mir
@pgindex @command{mds-mmds}
@cpindex Compatibility layer, Mir
@cpindex Mir compatibility layer
Should be added if you are running a
@command{mir}-to-@command{mds} server,
like @command{mds-mmds}.
@item wayland
@pgindex @command{mds-wmds}
@cpindex Compatibility layer, Wayland
@cpindex Wayland compatibility layer
Should be added if you are running a
@command{wayland}-to-@command{mds} server,
like @command{mds-wmds}.
@item x11
@pgindex @command{mds-xmds}
@cpindex Compatibility layer, X.org
@cpindex X.org compatibility layer
Should be added if you are running an
@command{X}-to-@command{mds} server, like
@command{mds-xmds}.
@end table



@node New Concepts
@chapter New Concepts

@menu
* Metadisplay Server::                        Goals and features and metadisplays.
@end menu



@node Metadisplay Server
@section Metadisplay Server

@cpindex Metadisplay server
@pgindex @code{mds-meta}
@cpindex Display server, meta
@cpindex Multi-display systems
A metadisplay server is a server that is connected to
one or more display server's simultaneously.
Additionally, it is acting as a display server on its
own. Any server, or even client, running in this
display will effectively be running in all of the
displays connected to the metadisplay.

The idea of the the metadisplay server came from the
idea of letting the user have the clipboard shared
across any number of @emph{selected} display server.
Rather than having a clipboard server written
specifically for this, it was seen as more
appropriate to have a server than could let any
server run inside any number of display server. Not
only will this let the user run any server this way.
It also makes it possible to run them across any
number of computers.

@pgindex @code{@command{mds-host}}
@pgindex @command{mds-remote}
@cpindex Networking
If a hosting server, like @command{mds-host}, runs
inside a metadisplay, any number of computers can
connect to the metadisplay using a server like
@command{mds-remote}. This creates a metadisplay
with multiple display from multiple computers. If a
clipboard server runs in this metadisplay, all of
these display on all of these computers will share
clipboard server.

Whilst not removing or degrading any functionality. A
negative property of this setup it that it is
centralised rather than distributed. If the computer
hosting the metadisplay crashes, the other computers
will no longer share this metadisplay, and lose the
connection to any server running in it.

In addition to a the clipboard server, there is a
host of other servers that makes sense to run in
multiple displays or across multiple computer:
drag-and-drop servers, human input device servers,
output servers, and even windowing servers.



@node Discussion
@chapter Discussion

@menu
* Server Architecture::                       Discussion on fundamental design choices.
* Fixing X.org Issues::                       Can we avoid the problems X.org has?
* Why Not Wayland::                           Why Wayland Won't Cut It.
* Why Not Mir::                               Why Mir Won't Cut It.
* Desktop Environments::                      What are desktop environments' relationship to mds?
@end menu



@node Server Architecture
@section Server Architecture

@cpindex Server architecture
@cpindex Architecture, servers
This chapter aims to enumerate advantages and
disadvantages with micro-display servers, traditional
monolithic display servers and other possible
designs. Please chime in with any insight.

@menu
* The Microserver Architecture::              The microserver architecture.
* The Monolithic Server Architecture::        The monolithic server architecture.
* The Hybrid Server Architecture::            The hybrid server architecture.
* The Megalithic Server Architecture::        The megalithic server architecture.
* The Modular Server Architecture::           The modular server architecture.
* The Modular Microserver Architecture::      The modular microserver architecture.
* The Exoserver Architecture::                The exoserver architecture.
@end menu



@node The Microserver Architecture
@subsection The Microserver Architecture

@cpindex Microserver architecture
@cpindex Architecture, microserver
@cpindex Microdisplay servers
Description: The display server is implement with
multiple binaries that speak with each other using a
well defined protocol.

@noindent
Implementations: mds.

@noindent
Advantages:

@itemize @bullet{}
@item
@cpindex Code quality
@cpindex Quality of code
Knowing the names of the servers you use and their
purpose makes it very easy to find where you want to
do patching in the source code.

@item
@cpindex Code quality
@cpindex Quality of code
Spaghetti code to a larger extent is virtually
impossible; the microserver architecture guarantees a
certain quality of the code architecture for the
display server.

@item
@cpindex Flexibility
If the message passing used in the display server
allows for message modification and retrieval
ordering, extending, modifying and using the display
server in unforeseen ways becomes much easier, and
will often not require any modifications to the
existing servers.

@item
@cpindex Flexibility
Replacing the display server is easier for a
micro-display server than it is for a monolithic
display server, because the servers could be replaced
one by one and could even support running under two
distinct protocol during the transitional period.

@item
@cpindex Code quality
@cpindex Quality of code
Not as many subprotocols needs to be defined. For
example, recording the output of the display does not
require a special protocol, one only needs to write a
server that listens on messages passed between
servers.

@item
@cpindex Stability
If a server crashes it does not crash the entire
session. Crashes can most often be repaired.

@item
@cpindex Flexibility
Because servers can easily be omitted and replaced
when starting the display server, it becomes much
easier to mount the display server on top of an
already running display server. For example, if you
want the performance of @code{weston} but then
flexibility and functionallity of @code{mds}, you
could start @code{mds} inside @code{weston} and
replace a small set of the servers with variants
written to running on top of Wayland; of course with
some functionallity of @code{mds} missing.

@item
@cpindex Security
It is trivial to only have setuid on for the part of
the display server where it is required.
@end itemize



@node The Monolithic Server Architecture
@subsection The Monolithic Server Architecture

@cpindex Monolithic server architecture
@cpindex Architecture, monolithic server
@cpindex Monolithic display servers
Description: The display server is implemented as one
binary.

@noindent
@cpindex X11
@cpindex X.org
@cpindex Mir
@cpindex Wayland
@cpindex Weston
@cpindex Surface Flinger
@cpindex Andriod/Linux, Surface Flinger
@cpindex Quartz Compositor
@cpindex Mac OS X, Quartz Compositor
@cpindex OS X, Quartz Compositor
@cpindex Desktop Window Manager
@cpindex Windows, Desktop Window Manager
Implementations: X11@footnote{X11 is a protocol, I
beleave all X11 servers are monolithic, atleast the
major ones are}, Mir, Wayland@footnote{Wayland is not
actually monolithic, it is just a protocol. But
Wayland is written with a monolithic mindset, and it
is preferred that the display server implementation
is monolithic.}, Surface Flinger, Quartz Compositor,
Desktop Window Manager.

@noindent
Advantages:

@itemize @bullet{}
@item
@cpindex Confidentiality
@cpindex Privacy
@cpindex Security
@cpindex Flexibility
The monolithic architecture makes it trivial to
isolate information for clients to achieve
confidentiality. Prioritising confidentiality however
leads to problems implementing features such as
screenshooting and global hotkeys.

@item
@cpindex Performance
Monolithic server does not need to pass messages
between modules, but can rather perform normal
function calls and achieve greater performance.

@item
@cpindex Size
Monolithic display servers can have a smaller memory
footprint than its full-fledged counterparts.
@end itemize



@node The Hybrid Server Architecture
@subsection The Hybrid Server Architecture

@cpindex Hybrid server architecture
@cpindex Architecture, hybrid server
@cpindex Hybrid display servers
@cpindex Milliserver architecture
@cpindex Architecture, milliserver
@cpindex Millidisplay servers
@cpindex Macroserver architecture
@cpindex Architecture, macroserver
@cpindex Macrodisplay servers
Description: The display server is implmeneted with
the microserver architecture except some components
are built into the master server for performance or
security reasons.

@noindent
Hybrid display server could arguably be called
milli-display servers to emphasis that they are
small, but not as small as micro-display servers, are
much more closely related to micro-display servers
than monolithic display servers, and, in constrast
with OS kernels, have a proper distinction from
monolithic systems and microsystems. @footnote{I
don't know about calling them macro-display servers,
that implies that they are the total opposite of
micro-display servers.}

@noindent
Implementations: none?

@noindent
Advantages:

@itemize @bullet{}
@item
Can achieve most of the microserver architecture's
advantages, but not always to the same extent.

@item
@cpindex Confidentiality
@cpindex Privacy
@cpindex Security
@cpindex Flexibility
By integrating some servers into the master server,
the hybrid architecture can isolate information for
clients to achieve confidentiality. Prioritising
confidentiality however leads to problems implementing
features such as screenshooting and global hotkeys.

@item
@cpindex Performance
Large and high frequency messages does not need to be
passed around to other servers if they are integrated
into the master server. This lets hybrid display
server achieve the same perfomance performance as
monolithic display servers for tasks where it is
desirable.
@end itemize

@noindent
The mds protocol and its reference implemention can
easily be made into a hybrid display server protocol
and an implementation thereof.



@node The Megalithic Server Architecture
@subsection The Megalithic Server Architecture

@cpindex Megalithic server architecture
@cpindex Architecture, megalithic server
@cpindex Megalithic display servers
@cpindex Megaserver architecture
@cpindex Architecture, megaserver
@cpindex Megadisplay servers
Description: A monolithic display server where
applications are loaded or compiled into the display
server itself.

@noindent
These are also known as mega-display servers.

@noindent
Implementations: none?

@noindent
Advantages:

@itemize @bullet{}
@item
@cpindex Performance
No interprocess communication is required, apart from
letting the display server know to load modules if it
does not compile in its programs. This lets megalithic
display server achieve even greater performance than
monolithic display servers.
@end itemize

@noindent
Disadvantages:

@itemize @bullet{}
@item
@cpindex Code quality
@cpindex Quality of code
Imposes restrictions on which languages applications
can use.

@item
@cpindex Flexibility
Imposes restrictions on how applications can behave.

@item
@cpindex Flexibility
@cpindex Code quality
@cpindex Quality of code
Cannot be networked without exposing an alternative
display server protocol.

@item
@cpindex Stability
The display becomes more crash prune; if an
application crashes it is likely to crash the entire
display.

@item
@cpindex Security
Applications will run with the same privileges as the
display server, which is root on most operating
systems.
@end itemize

@noindent
@cpindex Gaming
Megalithic display servers could be interesting for
high performing gaming consoles.



@node The Modular Server Architecture
@subsection The Modular Server Architecture

@cpindex Modular server architecture
@cpindex Architecture, modular server
@cpindex Modular display servers
Description: A monolithic display server where
server-like programs can be loaded as modules into
the display server but applicates are connected with
interprocess communication.

@noindent
Implementations: none?@footnote{Desktop Window Manager
is partially modular, but as of yet, this cannot be
utilised by end-users.}

@noindent
Advantages:

@itemize @bullet{}
@item
@cpindex Flexibility
Can achieve that flexibility of micro-display servers,
but not when networked, with the same memory footprint
as monolithic display servers.

@item
Has the same advantages as monolithic kernels.

@item
@cpindex Performance
Applications that require absolute performance can
be loaded as modules and achieve the same performance
as megalithic kernels, however with the same caveats.
@end itemize

@noindent
With a little work the mds protocol could be
transformed into a modular server display protocol,
and with some work the reference implementation could
be made into a modular server display.



@node The Modular Microserver Architecture
@subsection The Modular Microserver Architecture

@cpindex Modular microserver architecture
@cpindex Architecture, modular microserver
@cpindex Modular microdisplay servers
Description: A modular display server with a module
that enables clients to act as modules that
communicates via interprocess communication rather
than being loaded into the display server.

@noindent
Implementations: none?

@noindent
Advantages:

@itemize @bullet{}
@item
The modular microserver architecture seem to provide
all of the advantages of the other architecture but
none of the disadvantages. However, modules can still
crash and bring down the display server, but the idea
is to not load unstable modules but let the be
servers. Therefore exo-diplay server are slightly
more robust.
@end itemize

@noindent
With a little work the mds protocol could be
transformed into a modular server display protocol,
and with some work the reference implementation could
be made into a modular server display. Then the
untransformed version of @command{mds-server} could
be made into a module for the transformed version.



@node The Exoserver Architecture
@subsection The Exoserver Architecture

@cpindex Exoserver architecture
@cpindex Architecture, exoserver
@cpindex Exodisplay servers
Description: An exo-display server is a tiny display
server that attempts to let applications access the
underlaying system directly and implements basic
interprocess communication to let applications share
vital information and coordinate with each other.

@noindent
Implementations: none?

@noindent
Advantages:

@itemize @bullet{}
@item
@cpindex Performance
Can achieve the same performance as megalithic
display servers.

@item
@cpindex Stability
Can achieve the same robustness as micro-display
servers.
@end itemize

@noindent
Disadvantages:

@itemize @bullet{}
@item
@cpindex Flexibility
@cpindex Code quality
@cpindex Quality of code
Cannot be networked without exposing an alternative
display server protocol.
@end itemize

@noindent
Exo-display servers could be interesting for high
performing gaming consoles.



@node Fixing X.org Issues
@section Fixing X.org Issues

X.org is been critiqued for several shortcoming, some
of which have caused people to start on new display
servers to replace X.org. This chapter will list some
issues and discuss how they can be avoided in mds.

@menu
* Automatic Cleanup::                         Cleanup up after applications.
* Input Problems::                            Problems related to human input.
* Other Issues::                              Other issues in X.org.
@end menu



@node Automatic Cleanup
@subsection Automatic Cleanup

@cpindex Automatic cleanup
@cpindex Cleanup, automatic
@cpindex Resolution change
@cpindex Games
A common critique of X.org is that the monitor
resolution is not restored if a game change the
resolution and for some reason, for instance a
software crash, does not switch back before exiting.
This problem is not intrinsic to the protocol, but
rather because of a lacking protocol. You can run a
program like @command{xrandr} to change the monitor
resolution for the entirety of the session and
@command{xrandr} can exit when the resolution has
changed. This is how it should be. However, there is
no way to tell an X.org server to switch back if the
connection between the program and server is lost.
This is easily fixed by adding a lifespan parameter
as found in @ref{set-gamma}.

@cpindex Gamma correction
A similar critique of X.org is that gamma ramps are
not restored when an application exits. Either the
ones complaining about this do not understand why
gamma ramps exists, namely so you can calibrate the
monitor's output in respect to the colours, and just
think it is a way to make the video in games
brighter. Or they think we should have daemons
running idly to have gamma adjustments. Or, more
likely and more validly, its is poorly phrased and
they actually want a way for applications, like
games, to inform the display server to undo its
modifications to the gamma ramps when the program
exits. This is already supported by the mds protocol.



@node Input Problems
@subsection Input Problems

@cpindex Grab, input
@cpindex Keyboard, grab
@cpindex Mouse, grab
@cpindex Input grabbing
X11 allows programs to exclusively grab keyboard and
mouse input. When a program that does this misbehaves
or become unresponsive, you cannot do anything but
manage it from another computer or restart the
computer. In mds exclusively grabbing is achieved by
setting the client priority for the related message
to the highest priority. @footnote{If multiple
clients do this, it is arbitrary who gets the message
first and can stop the others from getting it.} This
is however not allowed (but nothing will stop you) as
the idea is that clients should either select a
predefined priority, select a priority between
servers it to be between, or select a priority of 50
percent or 150 percent of another servers priority.
Thus, unless a client breaks this rule, you can always
have your server for switching to the TTY at a higher
priority than other programs.

A similar, and probably related, problem in X.org is
that global keybindings don't work when a popup or
menu has focus. (Thankfully GTK+ will close that item
if it receives unexpected input.) I have hard time
seeing how this could become an issue in mds.

@cpindex Hotkeys
@cpindex Keyboard bindings
@cpindex Bindings, keyboard
@cpindex Keyboard shortcuts
@cpindex Shortcuts, keyboard
Another issue related to the keyboard in X.org is
that hotkeys in programs do not work in a few
situtations because the program was not designed with
another keyboard layout in mind than the keyboard
layout the developer used. I suggest that programs
restrain themself from including
@key{Alternative Graph} in their hotkeys and only use
@key{Shift} for @key{a} through @key{Z} and
@key{Space}. However, what I would really like to see
is that toolkits lets users modify all hotkeys. If
program additionally restrain themself to having all
hotkeys contain control or alt the keyboard layouts
with non-latin alphabets would not suffer because
they do not use the latin alphabet.



@node Other Issues
@subsection Other Issues

@cpindex Re-executing servers
@cpindex Updating, online
@cpindex Online updating
@cpindex Version update
@sgindex @code{SIGUSR1}
@sgindex @code{SIGUPDATE}
X11 display servers do not let you upgrade or
otherwise replace graphics drivers online. Or other
parts of it. X11 display servers could allow you to
send a signal, for instance @code{SIGUSR1}, to upgrade
the whole server, however this is not favourable, and
X.org does not do this. The reference implemention of
the mds protocol lets you safely upgrade any part of
it online by sending @code{SIGUSR1} to the server that
should be upgraded. On catastrophic failure in this
process the server would restart and lose volatile
data, but the server should be upgraded and it would
ask all running clients for resend information the
server lost.

@cpindex Threading
@cpindex Multi-threading
@cpindex Pervasively parallel processing
@cpindex Pervasive threading
Another issue with X.org is that it is not
multithreaded, which can cased intensive programs
to freeze your desktop. mds is inherently pervasively
parallel and only subsystems, rather than the whole
system, can suffer from this. It is however easy for
mds servers to implement pervasive threading, that
is, letting each request spin up a new thread in the
server.



@node Why Not Wayland
@section Why Not Wayland

@cpindex Wayland
Development of @command{mds} started out of concern
that Wayland would not meet our needs, and the
knowledge that X does not. We are now however aware
that Wayland meets our needs even less than X@.
@footnote{Not even counting that the documentation
for Wayland is way more lacking that X's
documentation.}

@cpindex Flexibility
Wayland only has protocols for drawing onto a buffer
and input devices, and some very limited output
protocols. Wayland is inherently inflexible. If
anyone wants to add additional functionally, must do
so in the compositor --- the window manager --- and
publish the protocol. It is then up to all other
compostors (window managers) to implement the
protocol.

It should be noted that Wayland does not even have an
official protocol for applying gamma corrects. Some
compositors (window managers) choose to implement it
by using @command{colord}.

Additionally, screenshooting, screen recording and
global hotkeys must be implemented in the compositor
(window manager). Why? Because of security. In
Wayland, security always trumps useability and
usefulness.

Another huge limitation of Wayland is that it does
not have any network protocol. For it to be network,
the compositor must implement a network protocol ---
and there is no official network protocol. When this
is all done, a compositor proxy must be written that
can communicate with it.



@node Why Not Mir
@section Why Not Mir

@cpindex Mir
The major problem with Mir, and why we need
@command{mds} instead, is that contributions to Mir
are subject Canonical's contributions-limiting
agreement (CLA).

@cpindex Flexibility
Mir, like Wayland, is very limited. Mir is however
easier to extend. Ignoring the CLA, Mir is better
Wayland, but for similar reasons it is still not
good enough.

Mir is however licensed under the GNU General Public
License version 3 and GNU Lesser General Public
License version 3. Much better than the MIT license,
and hopefully we can steal some stuff.



@node Desktop Environments
@section Desktop Environments

@cpindex Goals of @command{mds}
@cpindex Desktop environments
@cpindex Environment, desktop
A design goal of @command{mds} is to bring unity to
the graphical environment. Something desktop
environments traditionally have been impairing.
Traditionally a desktop environment would implement,
or implement some of:
@itemize @bullet{}
@item
Window layout management (window manager)
@item
Window decoration (window manager)
@item
Workspaces (window manager)
@item
Compositor (window manager)
@item
Taskbars
@item
Status icon trays
@item
Launchers
@item
Application menus
@item
Autostart of applications
@item
Keyboard bindings
@item
Rat bindings
@item
Rat barriers
@item
Desktop
@item
Widgets
@item
Their own display manager (login screen)
@item
Their own screensaver and screenlocker
@item
Their own graphical toolkit
@item
A bunch of random graphical tools
@end itemize

This is absolute madness, a waste of time and creates
fragmentation.

There is no problem for a desktop environment
development team to implement all this for their
desktop environment for @command{mds}. However doing
so is discourage for the mentioned reasons as well as
because doing so means that the user needs to know
what not to launch, that is, what the desktop
environment will start.

@menu
* Window Management::                         Window management in mds.
* Application Management::                    Application management in mds.
* Input Management::                          Management of input peripherals in mds.
* The Desktop::                               The desktop in mds.
@end menu



@node Window Management
@subsection Window Management

@cpindex Window management
@cpindex Widdow layout managers
@cpindex Hotkeys
@cpindex Keyboard bindings
@cpindex Bindings, keyboard
@cpindex Keyboard shortcuts
@cpindex Shortcuts, keyboard
@pgindex @command{mds-keybind}
For @command{mds}, a desktop environment should not
have its own window layout manager. A better solution
is to have a few well written window layout manager
that are different from each other in how windows are
layed out. These should not listen for keyboard
actions to figure out how it shall rearrange the
windows. Instead they should listen on the display
server's messaging system for such commands, and
@command{mds-keybind} or similar server should be
configured with all hotkeys.

@cpindex Window decorators
@cpindex Decorators, windows
There are a few classes of window decorator. A
desktop environment still do not need its own. They
can however create themes for existing decorators.
What we need here is a small set of window decorators
that are very customisable.

@cpindex Workspaces
@cpindex Pagers
Workspaces in X is poorly done. Window managers
implement it, and pagers are window manager dependent
@footnote{Well, there is Extended Window Manager
Hints (EWMH), but it is very restricted.}. Yet there
are very few properties they can have:
@itemize @bullet{}
@item
Do workspaces span outputs, screens or the display?
@item
Are workspaces dependent on outputs, screens or
displays?
@item
Do workspaces have a geometrical position?
@item
Are new workspaces created when needed?
@end itemize
Clearly what we need is one workspace manager where
these can be configured. And the desktop environments
can create their own pagers if they see fit, but all
pagers work everywhere.

@cpindex Compositors
@cpindex Fancy effects
@cpindex Effects, fancy
Traditionally desktop environments wrote their own
compositor for flash or otherwise fancy effects, or
write a quirks to a common one so the common on could
be used. With all other parts, of what has
traditionally be the window manager, independent of
the desktop environment, creating one universal
compositor with plugin support for effects the
desktop environment want to have, such be no problem.



@node Application Management
@subsection Application Management

@cpindex Application management
@cpindex Taskbars
@cpindex Extended Window Manager Hints
@cpindex EWMH (Extended Window Manager Hints)
Many X desktop environments provide taskbars, where
all windows are listed. However because of Extended
Window Manager Hints (EWMH), and the ability to read
windows' position and wait for windows to move, this
is not actually necessary. Of course, desktop
environments may need to do this to theme the
environment. A taskbar for @command{mds} should:
@itemize @bullet{}
@item
be about to restrict listed windows a those under
specific outputs, and
@item
be about to restrict listed windows to viewed
workspaces.
@end itemize

@cpindex Status icon tray
@cpindex System tray
@cpindex Tray, status icons
Traditionally, status icon trays have been
implemented with window embed method. And apart
from there being two competing standard, this is
pretty sane. But ther have been some restrictions
@command{mds} does not suffer:
@itemize @bullet{}
@item
icons should not be rearranged, and
@item
embedder did not know of the background looked where
the icon was added.
@end itemize

Desktop environments should feel free to create their
own themed application launchers and application
menus. This functionally is already de facto
standardised, and there is no reason to change
anything.

@cpindex Startup of applications, automatic
@cpindex Automatic startup of application
@cpindex Application, startup, automatic
@pgindex @file{mdsinitrc}
Some desktop environments provide a method to for
automatically starting applications during the
startup of a desktop environment. This is
discouraged. It is better to teach the user to edit
@file{~/.mdsinitrc}.



@node Input Management
@subsection Input Management

@cpindex Input management
@cpindex Window management
@cpindex Hotkeys
@cpindex Keyboard bindings
@cpindex Bindings, keyboard
@cpindex Keyboard shortcuts
@cpindex Shortcuts, keyboard
@pgindex @command{mds-keybind}
Many desktop environments and window managers for X
implement global keyboard bindings. This is not how
you should do this. The servers should recognise
commands passed via @command{mds}'s interprocess
communication. Configurations of the keyboard
bindings should be done in a server like
@command{mds-keybind}.

@pgindex @command{mds-ratbind}
@cpindex Rat bindings
@cpindex Mouse bindings
@cpindex Pointer bindings
@cpindex Hotcorners
@pgindex @command{mds-ratbarrier}
@cpindex Cursor barriers
@cpindex Rat pointer barriers
@cpindex Mouse pointer barriers
@cpindex Pointer barriers
@cpindex Screen edges, barriers
@cpindex Barriers, rat
Similarily some desktop environments implement rat
bindings@footnote{Notably hot corners.} and rat
barriers. This too should be done via servers like
like @command{mds-ratbind} and like
@command{mds-ratbarrier}.



@node The Desktop
@subsection The Desktop

@cpindex Desktop
@cpindex File manager
@cpindex Background
@cpindex Root window
@cpindex Window, root
Desktop environments provide their own desktop
because they want it to fit the rest of the
environment. For example, it can use components of
the desktop environment's file manager. This practice
is however problematic, because they also implement
the background, which is also implemented on top of
the root windows. @command{mds} desktops should use a
transparent background and let the root window be
used for implementing the background.

@cpindex Desktop widgets
@cpindex Widgets, desktop
Additionally, some desktop environments provide
desktop widgets. These can either be drawn on the
root window, the desktop window or as
always-on-bottom windows. In @command{mds}, windows
can have Z-order priority. That is, you can specify
how important it is that your window is at the bottom
or at the top. For widgets with input, it is
recommended to use this to put the widget just above
the desktop window. For windows without input, it is
recommended draw on the root windows. However doing so
requires that be listen for updates to the backgrund.



@node GNU General Public License
@appendix GNU General Public License
@include gpl.texinfo

@node GNU Free Documentation License
@appendix GNU Free Documentation License
@include fdl.texinfo

@node Program index
@unnumbered Program index
@printindex pg

@node Variable index
@unnumbered Variable index
@printindex vr

@node Option index
@unnumbered Option index
@printindex op

@node Concept index
@unnumbered Concept index
@printindex cp

@node Signal index
@unnumbered Signal index
@printindex sg

@node Function index
@unnumbered Function index
@printindex fn

@node Data type index
@unnumbered Data type index
@printindex tp

@node Unicode block index
@unnumbered Unicode block index
@printindex ub

@node Protocol index
@unnumbered Protocol index
@printindex pr


@bye


TODO toolkit guidelines
       screen reading
       keyboard commands
       rat commands
       look and feel
       configurations
TODO other input devices
       3d pointer
       joystick
       gamepad
       infrared remote
       steering wheel
       pedals
       gloves
       multitouch (screen, rat)
       acceleroscope
       gyroscope
       camera
       3d camera

TODO protocol: embed: embedding windows inside other windows such as a status icon tray
TODO protocol: arcade: a game takes over control over outputs for increased performance
TODO protocol: startup: a mechanism allowing a desktop environment to track application startup
TODO protocol: drag;; drag and drop should be usable for saving files.
TODO protocol: keytrans: changing keyboard layout
TODO protocol: rat
TODO protocol: cursor
TODO protocol: colour
TODO protocol: state
TODO protocol: focus;; multifocus
TODO protocol: compositor
TODO protocol: crtc
TODO protocol: presentation
TODO protocol: network
TODO protocol: decorator
TODO protocol: workspace
TODO protocol: ping

TODO notifications (balloons, bubbles)
TODO virtual resolution (the screen is larger than the output)

TODO taskbar features:
  progress bars (any number) with colours
  control buttons such as play, pause, previous and next
  urgency alert
  stack all windows that belongs to the same process
  stack all windows with the same class
  extensible right-click menu
  right-click menu includes actions to start a new process

TODO application menu features:
  different ways to start an program, for example,
    browers may include a safe-browsing mode.

TODO In `Rat Cursors` use anchors and references to hyperlink names.

TODO Indices:
  Protocols