code: func PropValWindows(reply *xproto.GetPropertyReply,
  	err error) ([]xproto.Window, error) {
  
  	if err != nil {
  		return nil, err
  	}
  	if reply.Format != 32 {
  		return nil, fmt.Errorf("PropValIds: Expected format 32 but got %d",
  			reply.Format)
  	}
  
  	ids := make([]xproto.Window, reply.ValueLen)
  	vals := reply.Value
  	for i := 0; len(vals) >= 4; i++ {
  		ids[i] = xproto.Window(xgb.Get32(vals))
  		vals = vals[4:]
  	}
  	return ids, nil
  }
docs: // PropValWindows is the same as PropValWindow, except that it returns a slice
  // of identifiers. Also must be 32 bit format.