code: func checkInternalName(fqdn string) bool {
  	if ip := net.ParseIP(fqdn); ip != nil {
  		return checkInternalIP(ip)
  	}
  
  	suffix := strings.Split(strings.ToLower(fqdn), ".")
  	_, icann := psl.PublicSuffix(suffix[len(suffix)-1])
  	if icann {
  		return false
  	}
  	return true
  }
docs: // All official domain suffixes are registered by icann, but because some
  // subdomains are not only check against the last part of the fqdn.