code: func (d *ulReqDecoder) error(format string, a ...interface{}) {
  	msg := fmt.Sprintf(
  		"pkt-line %d: %s", d.nLine,
  		fmt.Sprintf(format, a...),
  	)
  
  	d.err = NewErrUnexpectedData(msg, d.line)
  }
docs: // fills out the parser stiky error