code: func PropValNum(reply *xproto.GetPropertyReply, err error) (uint, error) {
  	if err != nil {
  		return 0, err
  	}
  	if reply.Format != 32 {
  		return 0, fmt.Errorf("PropValNum: Expected format 32 but got %d",
  			reply.Format)
  	}
  	return uint(xgb.Get32(reply.Value)), nil
  }
docs: // PropValNum transforms a GetPropertyReply struct into an unsigned
  // integer. Useful when the property value is a single integer.