string $tempName: filesystem path to the temporary file for checks
string &$error: output: HTML error to show if upload canceled by returning false
+'UserCan': To interrupt the "user can do X to Y article" check
+$title: Title object being checked against
+$user : Current user object
+$action: Action being checked
+$result: Pointer to result returned if hook returns false
+
'UserCreateForm': change to manipulate the login form
$template: SimpleTemplate instance for the form