code: func ParseStringShort(input string) (*Durafmt, error) {
  	if input == "0" || input == "-0" {
  		return nil, errors.New("durafmt: missing unit in duration " + input)
  	}
  	duration, err := time.ParseDuration(input)
  	if err != nil {
  		return nil, err
  	}
  	return &Durafmt{duration, input, true}, nil
  }
docs: // ParseStringShort creates a new *Durafmt struct from a string, short form
  // returns an error if input is invalid.