===== RFC5234 - Augmented BNF for Syntax Specifications: ABNF =====
[[dido:public:ra:xapend:xapend.b_stds:tech:ietf:start| return to the IETF Standards ]]

<table>
<caption>Data sheet for RFC5234 Augmented BNF for Syntax Specifications: ABNF (ABNF)</caption>
| Title                      | Augmented BNF for Syntax Specifications: ABNF |
| Acronym                    | ABNF |
| Version                    | 2008 |
| Document Number            | RFC5234 |
| Release Date               | January 2004 |
| Reference                  | [[https://tools.ietf.org/html/rfc5234]] |''
| Notes                      | Also see [[dido:public:ra:xapend:xapend.b_stds:tech:ietf:7405]] |
</table>

  : **Note**: The following is an excerpt from the official IETF RFC. It is provided here as a convenience and is not authoritative. Refer to the original document as the authoritative reference.


==== Introduction ====
//Internet technical specifications often need to define a formal
[[dido:public:ra:xapend:xapend.a_glossary:s:syntax|syntax]] and are free to employ whatever notation their authors deem
useful.  Over the years, a modified version of [[dido:public:ra:xapend:xapend.a_glossary:b:bnf]], called Augmented BNF (ABNF), has been popular among many
[[dido:public:ra:xapend:xapend.a_glossary:i:internet|Internet]] specifications.  It balances compactness and simplicity with
reasonable representational power.  In the early days of the Arpanet,
each specification contained its own definition of ABNF.  This
included the email specifications, [RFC733] and then [RFC822], which
came to be the common citations for defining ABNF.  The current
document separates those definitions to permit selective reference.
Predictably, it also provides some modifications and enhancements.//

//The differences between standard BNF and ABNF involve naming rules,
repetition, alternatives, order-independence, and value ranges.
Appendix B supplies rule definitions and encoding for a core lexical
analyzer of the type common to several Internet specifications.  It
is provided as a convenience and is otherwise separate from the meta
language defined in the body of this document, and separate from its
formal status.//

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