code: func checkAuthoritativeNss(fqdn, value string, nameservers []string) (bool, error) {
  	for _, ns := range nameservers {
  		r, err := dnsQuery(fqdn, dns.TypeTXT, []string{net.JoinHostPort(ns, "53")}, false)
  		if err != nil {
  			return false, err
  		}
  
  		if r.Rcode != dns.RcodeSuccess {
  			return false, fmt.Errorf("NS %s returned %s for %s", ns, dns.RcodeToString[r.Rcode], fqdn)
  		}
  
  		var records []string
  
  		var found bool
  		for _, rr := range r.Answer {
  			if txt, ok := rr.(*dns.TXT); ok {
  				record := strings.Join(txt.Txt, "")
  				records = append(records, record)
  				if record == value {
  					found = true
  					break
  				}
  			}
  		}
  
  		if !found {
  			return false, fmt.Errorf("NS %s did not return the expected TXT record [fqdn: %s, value: %s]: %s", ns, fqdn, value, strings.Join(records, " ,"))
  		}
  	}
  
  	return true, nil
  }
docs: // checkAuthoritativeNss queries each of the given nameservers for the expected TXT record.