'AbortDiffCache': Can be used to cancel the caching of a diff
&$diffEngine: DifferenceEngine object
+'AbortEmailNotification': Can be used to cancel email notifications for an edit.
+$editor: The User who made the change.
+$title: The Title of the page that was edited.
+
'AbortLogin': Return false to cancel account login.
$user: the User object being authenticated against
$password: the password being submitted, not yet checked for validity