code: func Generate(xu *xgbutil.XUtil) (*Window, error) {
  	wid, err := xproto.NewWindowId(xu.Conn())
  	if err != nil {
  		return nil, err
  	}
  	return New(xu, wid), nil
  }
docs: // Generate is just like New, but generates a new X resource id for you.
  // Geom is initialized to (0, 0) 1x1.
  // It is possible for id generation to return an error, in which case, an
  // error is returned here.