code: func (d Dnssec) nsec(name, zone string, ttl, incep, expir uint32) ([]dns.RR, error) {
  	nsec := &dns.NSEC{}
  	nsec.Hdr = dns.RR_Header{Name: name, Ttl: ttl, Class: dns.ClassINET, Rrtype: dns.TypeNSEC}
  	nsec.NextDomain = "\\000." + name
  	nsec.TypeBitMap = []uint16{dns.TypeRRSIG, dns.TypeNSEC}
  
  	sigs, err := d.sign([]dns.RR{nsec}, zone, ttl, incep, expir)
  	if err != nil {
  		return nil, err
  	}
  
  	return append(sigs, nsec), nil
  }
docs: // nsec returns an NSEC useful for NXDOMAIN respsones.
  // See https://tools.ietf.org/html/draft-valsorda-dnsop-black-lies-00
  // For example, a request for the non-existing name a.example.com would
  // cause the following NSEC record to be generated:
  //	a.example.com. 3600 IN NSEC \000.a.example.com. ( RRSIG NSEC )
  // This inturn makes every NXDOMAIN answer a NODATA one, don't forget to flip
  // the header rcode to NOERROR.