code: def has_submenu_items(self, current_page, allow_repeating_parents,
                            original_menu_tag, menu_instance=None, request=None):
          
          return menu_instance.page_has_children(self)
docs: When rendering pages in a menu template a `has_children_in_menu`
          attribute is added to each page, letting template developers know
          whether or not the item has a submenu that must be rendered.
  
          By default, we return a boolean indicating whether the page has
          suitable child pages to include in such a menu. But, if you are
          overriding the `modify_submenu_items` method to programatically add
          items that aren't child pages, you'll likely need to alter this method
          too, so the template knows there are sub items to be rendered.