code: func HasValidTLD(domain string, when time.Time) bool {
  	labels := strings.Split(strings.ToLower(domain), ".")
  	rightLabel := labels[len(labels)-1]
  	// if the rightmost label is not present in the tldMap, it isn't valid and
  	// never was.
  	if tldPeriod, present := tldMap[rightLabel]; !present {
  		return false
  	} else if tldPeriod.Valid(when) != nil {
  		// If the TLD exists but the date is outside of the gTLD's validity period
  		// then it is not a valid TLD.
  		return false
  	}
  	// Otherwise the TLD exists, and was a valid TLD delegated in the root DNS
  	// at the time of the given date.
  	return true
  }
docs: // HasValidTLD checks that a domain ends in a valid TLD that was delegated in
  // the root DNS at the time specified.