docs: def add_item(self, item, field_name=None):
          """
          Add the item to the specified section.
  
          Intended for use with items of settings.ARMSTRONG_SECTION_ITEM_MODEL.
          Behavior on other items is undefined.
          """
          field_name = self._choose_field_name(field_name)
          related_manager = getattr(item, field_name)
          related_manager.add(self)