code: func WmIconSet(xu *xgbutil.XUtil, win xproto.Window, icons []WmIcon) error {
  	raw := make([]uint, 0, 10000) // start big
  	for _, icon := range icons {
  		raw = append(raw, icon.Width, icon.Height)
  		raw = append(raw, icon.Data...)
  	}
  
  	return xprop.ChangeProp32(xu, win, "_NET_WM_ICON", "CARDINAL", raw...)
  }
docs: // _NET_WM_ICON set