code: func (i *ID) UnmarshalJSON(b []byte) (err error) {
  	var id uint64
  	if len(b) < 3 {
  		return nil
  	}
  	id, err = strconv.ParseUint(string(b[1:len(b)-1]), 16, 64)
  	*i = ID(id)
  	return err
  }
docs: // UnmarshalJSON deserializes an ID type (SpanID, ParentSpanID) from HEX.