code: func ChangeProp(xu *xgbutil.XUtil, win xproto.Window, format byte, prop string,
  	typ string, data []byte) error {
  
  	propAtom, err := Atm(xu, prop)
  	if err != nil {
  		return err
  	}
  
  	typAtom, err := Atm(xu, typ)
  	if err != nil {
  		return err
  	}
  
  	return xproto.ChangePropertyChecked(xu.Conn(), xproto.PropModeReplace, win,
  		propAtom, typAtom, format,
  		uint32(len(data)/(int(format)/8)), data).Check()
  }
docs: // ChangeProperty abstracts the semi-nastiness of xgb.ChangeProperty.