code: func (fp *fieldPath) String() string {
  	ss := make([]string, fp.last+1)
  	for i := 0; i <= fp.last; i++ {
  		ss[i] = strconv.Itoa(fp.path[i])
  	}
  	return strings.Join(ss, "/")
  }
docs: // String returns a string representing the fieldPath