code: func escapeTag(tag reflect.StructTag) string {
  	t := string(tag)
  	if strings.ContainsRune(t, '`') {
  		// there are ` in the string; we can't use ` to enclose the string
  		return strconv.Quote(t)
  	}
  	return "`" + t + "`"
  }
docs: // escape a struct field tag string back to source code