code: async def container_val(self, elem, container_type, params=None):
          
          if hasattr(container_type, "serialize_archive"):
              raise ValueError("not supported")
          if self.writing:
              return await self._dump_container_val(
                  self.iobj, elem, container_type, params
              )
          else:
              raise ValueError("Not supported")
docs: Single cont value
          :param elem:
          :param container_type:
          :param params:
          :return: