code: func (es *eventStream) sendUserEvent(ue serf.UserEvent) error {
  	header := responseHeader{
  		Seq:   es.seq,
  		Error: "",
  	}
  	rec := userEventRecord{
  		Event:    ue.EventType().String(),
  		LTime:    ue.LTime,
  		Name:     ue.Name,
  		Payload:  ue.Payload,
  		Coalesce: ue.Coalesce,
  	}
  	return es.client.Send(&header, &rec)
  }
docs: // sendUserEvent is used to send a single user event