Based on an excerpt from Anomie's IRC conversation with me.
Change-Id: I02661548a30fd40eaa72d77c98a6801dbbaff456
/**
* 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
*/