RFC 2234 (rfc2234) - Page 2 of 14

Augmented BNF for Syntax Specifications: ABNF

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