code: func WmSyncRequestExtra(xu *xgbutil.XUtil, win xproto.Window, reqNum uint64,
  	time xproto.Timestamp) error {
  
  	syncReq, err := xprop.Atm(xu, "_NET_WM_SYNC_REQUEST")
  	if err != nil {
  		return err
  	}
  
  	high := int(reqNum >> 32)
  	low := int(reqNum<<32 ^ reqNum)
  
  	return ClientEvent(xu, win, "WM_PROTOCOLS", int(syncReq), int(time),
  		low, high)
  }
docs: // _NET_WM_SYNC_REQUEST req extra