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RFC 4234: Augmented BNF for Syntax Specifications: ABNF

This RFC has been replaced. Do not implement against it for new work — it was formally obsoleted by RFC 5234.

Current document in this lineage: RFC 5234 — Augmented BNF for Syntax Specifications: ABNF

In plain English — editorial summary, not part of the RFC

Internet technical specifications often need to define a formal syntax. Over the years, a modified version of Backus-Naur Form (BNF), called Augmented BNF (ABNF), has been popular among many Internet specifications. The current specification documents ABNF. It balances compactness and simplicity, with reasonable representational power. The differences between standard BNF and ABNF involve naming rules, repetition, alternatives, order-independence, and value ranges. This specification also supplies additional rule definitions and encoding for a core lexical analyzer of the type common to several Internet specifications. [STANDARDS-TRACK]

Document record

Document ID
RFC4234
Published
October 2005
Authors
D. Crocker; P. Overell
Status
DRAFT STANDARD
Stream
IETF
Area
—
Pages
16
Also known as
—
Obsoletes:
RFC 2234
Obsoleted by:
RFC 5234

Topics

Standards lineage

This document is one revision in a chain of 3 RFCs, each formally replacing the one before it.

  1. RFC 2234 (1997)
  2. RFC 4234 (2005)
  3. RFC 5234 (2008) ✓

Read the full history of Augmented BNF for Syntax Specifications: ABNF →

Referenced by

One later RFC formally updates or obsoletes part of this document.

Related documents

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The document record above — title, authors, date, status, stream, area, relationships, DOI and errata — is imported verbatim from the public RFC Editor index. The “in plain English” section is editorial: written by The metasystema editorial team, not part of the RFC. Where the two differ, the RFC text governs.

Last checked against the RFC Editor index on . RFCs are never revised after publication; changes are issued as new documents.

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canonical URL: /rfc/4234-augmented-bnf-for-syntax-specifications-abnf