code: func (d PrettyDuration) String() string {
  	label := fmt.Sprintf("%v", time.Duration(d))
  	if match := prettyDurationRe.FindString(label); len(match) > 4 {
  		label = strings.Replace(label, match, match[:4], 1)
  	}
  	return label
  }
docs: // String implements the Stringer interface, allowing pretty printing of duration
  // values rounded to three decimals.