code: func (a *Agent) UserEvent(name string, payload []byte, coalesce bool) error {
  	a.logger.Printf("[DEBUG] agent: Requesting user event send: %s. Coalesced: %#v. Payload: %#v",
  		name, coalesce, string(payload))
  	err := a.serf.UserEvent(name, payload, coalesce)
  	if err != nil {
  		a.logger.Printf("[WARN] agent: failed to send user event: %v", err)
  	}
  	return err
  }
docs: // UserEvent sends a UserEvent on Serf, see Serf.UserEvent.