code: func ActivePID(pid int32, args ...int) error {
  	if xu == nil {
  		var err error
  		xu, err = xgbutil.NewConn()
  		if err != nil {
  			return err
  		}
  	}
  
  	if len(args) > 0 {
  		err := ewmh.ActiveWindowReq(xu, xproto.Window(pid))
  		if err != nil {
  			return err
  		}
  
  		return nil
  	}
  
  	// get the xid from pid
  	xid, err := GetXidFromPid(xu, pid)
  	if err != nil {
  		return err
  	}
  
  	err = ewmh.ActiveWindowReq(xu, xid)
  	if err != nil {
  		return err
  	}
  
  	return nil
  }
docs: // ActivePID active the window by PID,
  //
  // If args[0] > 0 on the Windows platform via a window handle to active,
  // If args[0] > 0 on the unix platform via a xid to active