http://www.rfc-editor.org/rfc/rfc2915.txt
RFC 2915: The Naming Authority Pointer (NAPTR) DNS Resource Record, M. Mealling, R. Daniel2000-09-01T23:00:00-00:00This document describes a Domain Name System (DNS) resource record which specifies a regular expression based rewrite rule that, when applied to an existing string, will produce a new domain label or Uniform Resource Identifier (URI). [STANDARDS-TRACK]