code: func PropValWindow(reply *xproto.GetPropertyReply,
  	err error) (xproto.Window, error) {
  
  	if err != nil {
  		return 0, err
  	}
  	if reply.Format != 32 {
  		return 0, fmt.Errorf("PropValId: Expected format 32 but got %d",
  			reply.Format)
  	}
  	return xproto.Window(xgb.Get32(reply.Value)), nil
  }
docs: // PropValWindow transforms a GetPropertyReply struct into an X resource
  // window identifier.
  // The property reply must be in 32 bit format.