code: func WmClassSet(xu *xgbutil.XUtil, win xproto.Window, class *WmClass) error {
  	raw := make([]byte, len(class.Instance)+len(class.Class)+2)
  	copy(raw, class.Instance)
  	copy(raw[(len(class.Instance)+1):], class.Class)
  
  	return xprop.ChangeProp(xu, win, 8, "WM_CLASS", "STRING", raw)
  }
docs: // WM_CLASS set