code: def serialize_task_id(self):
          
          return "{}@{}".format(
              self._identification[TASK_UUID_FIELD],
              self._nextTaskLevel().toString()).encode("ascii")
docs: Create a unique identifier for the current location within the task.
  
          The format is C{b"<task_uuid>@<task_level>"}.
  
          @return: L{bytes} encoding the current location within the task.