code: func (d *Duration) UnmarshalJSON(buf []byte) error {
  	var str string
  
  	err := json.Unmarshal(buf, &str)
  	if err != nil {
  		return err
  	}
  
  	dur, err := time.ParseDuration(str)
  	if err != nil {
  		return err
  	}
  
  	d.Duration = dur
  	return nil
  }
docs: // UnmarshalJSON decodes a Duration from a JSON string parsed using time.ParseDuration.