add special support for LIBGAMMA_DEVICE_REQUIRE_GROUP in libgamma_perror

Signed-off-by: Mattias Andrée <maandree@operamail.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/src/libgamma-error.h b/src/libgamma-error.h
index 1591fe1..06a7077 100644
--- a/src/libgamma-error.h
+++ b/src/libgamma-error.h
@@ -297,7 +297,10 @@ extern const char* libgamma_group_name;
  * used to print the current error stored in `errno`.
  * If `error_code` is non-negative (an `errno` value`), that
  * value will be stored in `errno` and `perror` will be
- * used to print it.
+ * used to print it. Additionally, if the `error_code` is
+ * the value of `LIBGAMMA_DEVICE_REQUIRE_GROUP` the
+ * required group will be printed with its numerical value
+ * and, if known, its name.
  * 
  * @param  name   The text to add at the beginning.
  * @param  value  The error code, may be an `errno` value.