code: func (j *JSON) String(name string) (string, error) {
  	v, err := j.value(name)
  	if err != nil {
  		return "", err
  	}
  
  	s, ok := v.(string)
  	if !ok {
  		return "", errors.New(fmt.Sprintf("unable to cast %T", v))
  	}
  
  	return s, nil
  }
docs: // String returns a string if it exists within the marshalled JSON io.Reader.