RFC 2234EditCreated 2007-06-05, updated 2017-05-18RFC 2234 is an RFC describing the "Augmented BNF for Syntax Specifications: ABNF". ABNF is widely used, including in other RFCs (such as RFC 2822 and RFC 3986, for example). See also Full text of RFC 2234: http://www.ietf.org/rfc/rfc2234.txt rfcswiki