ApiMessage: Improve documentation

Based on an excerpt from Anomie's IRC conversation with me.

Change-Id: I02661548a30fd40eaa72d77c98a6801dbbaff456

diff --git a/includes/api/ApiMessage.php b/includes/api/ApiMessage.php
index db826a6..370911a 100644 (file)
--- a/includes/api/ApiMessage.php
+++ b/includes/api/ApiMessage.php
@@ -23,6 +23,12 @@
 
 /**
  * Interface for messages with machine-readable data for use by the API
+ *
+ * The idea is that it's a Message that has some extra data for the API to use when interpreting it
+ * as an error (or, in the future, as a warning). Internals of MediaWiki often use messages (or
+ * message keys, or Status objects containing messages) to pass information about errors to the user
+ * (see e.g. Title::getUserPermissionsErrors()) and the API has to make do with that.
+ *
  * @since 1.25
  * @ingroup API
  */