RFC 2234 (rfc2234) - Page 1 of 14
Augmented BNF for Syntax Specifications: ABNF
Alternative Format: Original Text Document
Network Working Group D. Crocker, Ed.
Request for Comments: 2234 Internet Mail Consortium
Category: Standards Track P. Overell
Demon Internet Ltd.
November 1997
Augmented BNF for Syntax Specifications: ABNF
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (1997). All Rights Reserved.
TABLE OF CONTENTS
1. INTRODUCTION .................................................. 2
2. RULE DEFINITION ............................................... 2
2.1 RULE NAMING .................................................. 2
2.2 RULE FORM .................................................... 3
2.3 TERMINAL VALUES .............................................. 3
2.4 EXTERNAL ENCODINGS ........................................... 5
3. OPERATORS ..................................................... 5
3.1 CONCATENATION RULE1 RULE2 ............................. 5
3.2 ALTERNATIVES RULE1 / RULE2 ................................... 6
3.3 INCREMENTAL ALTERNATIVES RULE1 =/ RULE2 .................... 6
3.4 VALUE RANGE ALTERNATIVES %C##-## ........................... 7
3.5 SEQUENCE GROUP (RULE1 RULE2) ................................. 7
3.6 VARIABLE REPETITION *RULE .................................... 8
3.7 SPECIFIC REPETITION NRULE .................................... 8
3.8 OPTIONAL SEQUENCE [RULE] ..................................... 8
3.9 ; COMMENT .................................................... 8
3.10 OPERATOR PRECEDENCE ......................................... 9
4. ABNF DEFINITION OF ABNF ....................................... 9
5. SECURITY CONSIDERATIONS ....................................... 10
Crocker & Overell Standards Track