code: func WmClassGet(xu *xgbutil.XUtil, win xproto.Window) (*WmClass, error) {
  	raw, err := xprop.PropValStrs(xprop.GetProperty(xu, win, "WM_CLASS"))
  	if err != nil {
  		return nil, err
  	}
  	if len(raw) != 2 {
  		return nil,
  			fmt.Errorf("WmClass: Two string make up WM_CLASS, but "+
  				"xgbutil found %d in '%v'.", len(raw), raw)
  	}
  
  	return &WmClass{
  		Instance: raw[0],
  		Class:    raw[1],
  	}, nil
  }
docs: // WM_CLASS get