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

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())))