docs: def get_all_leaves(self, item_ids=None, language=None, forbidden_item_ids=None):
          """
          Get all leaves reachable from the given set of items. Leaves having
          inactive relations to other items are omitted.
  
          Args:
              item_ids (list): items which are taken as roots for the reachability
              language (str): if specified, filter out items which are not
                  available in the given language
  
          Returns:
              set: leaf items which are reachable from the given set of items
          """
          return sorted(set(flatten(self.get_leaves(item_ids, language=language, forbidden_item_ids=forbidden_item_ids).values())))