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
