code: def _start(self, fields):
          
          fields[ACTION_STATUS_FIELD] = STARTED_STATUS
          fields.update(self._identification)
          if self._serializers is None:
              serializer = None
          else:
              serializer = self._serializers.start
          Message(fields, serializer).write(self._logger, self)
docs: Log the start message.
  
          The action identification fields, and any additional given fields,
          will be logged.
  
          In general you shouldn't call this yourself, instead using a C{with}
          block or L{Action.finish}.