&$join_conds: join conditions for the tables
$opts: FormOptions for this request
+'LoginUserMigrated': Called during login to allow extensions the opportunity to
+inform a user that their username doesn't exist for a specific reason, instead
+of letting the login form give the generic error message that the account does
+not exist. For example, when the account has been renamed or deleted.
+$user: the User object being authenticated against.
+&$msg: the message identifier for abort reason, or an array to pass a message
+ key and parameters.
+
'Collation::factory': Called if $wgCategoryCollation is an unknown collation.
$collationName: Name of the collation in question
&$collationObject: Null. Replace with a subclass of the Collation class that