* 1.27+: IApiMessage, or a key or key+parameters in ApiBase::$messageMap.
* Earlier: A key or key+parameters in ApiBase::$messageMap.
+'ApiDeprecationHelp': Add messages to the 'deprecation-help' warning generated
+from ApiBase::addDeprecation().
+&$msgs: Message[] Messages to include in the help. Multiple messages will be
+ joined with spaces.
+
'APIEditBeforeSave': DEPRECATED! Use EditFilterMergedContent instead.
Before saving a page with api.php?action=edit, after
processing request parameters. Return false to let the request fail, returning