RFC 2234 (rfc2234) - Page 2 of 14
Augmented BNF for Syntax Specifications: ABNF
Alternative Format: Original Text Document
RFC 2234 ABNF for Syntax Specifications November 1997
6. APPENDIX A - CORE ............................................. 11
6.1 CORE RULES ................................................... 11
6.2 COMMON ENCODING .............................................. 12
7. ACKNOWLEDGMENTS ............................................... 12
8. REFERENCES .................................................... 13
9. CONTACT ....................................................... 13
10. FULL COPYRIGHT STATEMENT ..................................... 14
1. INTRODUCTION
Internet technical specifications often need to define a format
syntax and are free to employ whatever notation their authors deem
useful. Over the years, a modified version of Backus-Naur Form
(BNF), called Augmented BNF (ABNF), has been popular among many
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, RFC 733 and then RFC 822 which
have come to be the common citations for defining ABNF. The current
document separates out that definition, 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 A (Core) 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.
2. RULE DEFINITION
2.1 Rule Naming
The name of a rule is simply the name itself; that is, a sequence of
characters, beginning with an alphabetic character, and followed by
a combination of alphabetics, digits and hyphens (dashes).
NOTE: Rule names are case-insensitive
The names , , and all refer
to the same rule.
Crocker & Overell Standards Track