code: func (callback ButtonReleaseFun) Connect(xu *xgbutil.XUtil, win xproto.Window,
  	buttonStr string, sync bool, grab bool) error {
  
  	return connect(xu, callback, xevent.ButtonRelease, win, buttonStr,
  		sync, grab)
  }
docs: // If 'sync' is True, then no further events can be processed until the
  // grabbing client allows them to be. (Which is done via AllowEvents. Thus,
  // if sync is True, you *must* make some call to AllowEvents at some
  // point, or else your client will lock.)