def __init__(self):
return TemplateSyntaxError.__init__(
self,
("The 'sub_menu' tag can only be used in menu templates to render "
"parts of other menus, initiated by calling one of the other "
"included tags: 'main_menu', 'flat_menu', 'section_menu' or "
"'children_menu' (custom tags are not supported). You might "
"want to update your template to use the 'children_menu' tag "
"instead."))
