code: func IsDNS1123Subdomain(value string) []string {
  	var errs []string
  	if len(value) > DNS1123SubdomainMaxLength {
  		errs = append(errs, MaxLenError(DNS1123SubdomainMaxLength))
  	}
  	if !dns1123SubdomainRegexp.MatchString(value) {
  		errs = append(errs, RegexError(dns1123SubdomainErrorMsg, dns1123SubdomainFmt, "example.com"))
  	}
  	return errs
  }
docs: // IsDNS1123Subdomain tests for a string that conforms to the definition of a
  // subdomain in DNS (RFC 1123).