code: def as_task(self, logger=None, **fields):
          
          return self._startTask(
              logger, self.action_type, self._serializers, **fields)
docs: Start a new L{eliot.Action} of this type as a task (i.e. top-level
          action) with the given start fields.
  
          See L{ActionType.__call__} for example of usage.
  
          @param logger: A L{eliot.ILogger} provider to which the action's
              messages will be written, or C{None} to use the default one.
  
          @param fields: Extra fields to add to the message.
  
          @rtype: L{eliot.Action}