code: func GrabChecked(xu *xgbutil.XUtil, win xproto.Window,
  	mods uint16, key xproto.Keycode) error {
  
  	var err error
  	for _, m := range xevent.IgnoreMods {
  		err = xproto.GrabKeyChecked(xu.Conn(), true, win, mods|m, key,
  			xproto.GrabModeAsync, xproto.GrabModeAsync).Check()
  		if err != nil {
  			return err
  		}
  	}
  	return nil
  }
docs: // GrabChecked Grabs a key with mods on a particular window.
  // This is the same as Grab, except that it issue a checked request.
  // Which means that an error could be returned and handled on the spot.
  // (Checked requests are slower than unchecked requests.)
  // This will also grab all combinations of modifiers found in xevent.IgnoreMods.