code: func (n *IP4Net) UnmarshalJSON(j []byte) error {
  	j = bytes.Trim(j, "\"")
  	if _, val, err := net.ParseCIDR(string(j)); err != nil {
  		return err
  	} else {
  		*n = FromIPNet(val)
  		return nil
  	}
  }
docs: // json.Unmarshaler impl