code: func xSource(X *xgbutil.XUtil) {
  	i := 1
  	for {
  		ewmh.ClientEvent(X, X.RootWin(), "NOOP", i)
  		i++
  		time.Sleep(200 * time.Millisecond)
  	}
  }
docs: // sendClientMessages is a goroutine that sends client messages to the root
  // window. We then listen to them later as a demonstration of responding to
  // X events. (They are sent with SubstructureNotify and SubstructureRedirect
  // masks set. So in order to receive them, we'll have to explicitly listen
  // to events of that type on the root window.)