http://www.rfc-editor.org/rfc/rfc3845.txt
RFC 3845: DNS Security (DNSSEC) NextSECure (NSEC) RDATA Format, J. Schlyter2004-08-01T23:00:00-00:00This document redefines the wire format of the "Type Bit Map" field in the DNS NextSECure (NSEC) resource record RDATA format to cover the full resource record (RR) type space. [STANDARDS-TRACK]