Comprehensive Core Rules and References for ABNF

Document Type Active Internet-Draft (individual in art area)
Last updated 2017-03-13
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Network Working Group                                         S. Leonard
Internet-Draft                                             Penango, Inc.
Updates: 5234 (if approved)                               March 13, 2017
Intended Status: Standards Track                                        
Expires: September 14, 2017                                             

            Comprehensive Core Rules and References for ABNF

   This document extends the base definition of ABNF (Augmented Backus-
   Naur Form) to include a reference syntax, along with core rules that
   provide comprehensive support for certain symbols related to ASCII.

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Leonard                     Standards Track                     [Page 1]
Internet-Draft              More Core Rules                   March 2017

1.  Introduction

   Augmented Backus-Naur Form (ABNF) [RFC5234] is a formal syntax that
   is popular among many Internet specifications. Many Internet
   documents employ this syntax along with the Core Rules defined in
   Appendix B.1 of [RFC5234]. However, the Core Rules do not specify
   many symbols in the ASCII range that are also needed by these relying
   documents, forcing document authors to define them as local rules.
   Sometimes different documents define these common symbols in
   different ways, resulting in confusion or incompatibility when the
   rules are misread or are combined with other sets of rules.
   Furthermore, [RFC5234] does not clarify whether referencing [RFC5234]
   for ABNF automatically defines its Core Rules.

   [RFC5234] also lacks a syntax for referring to rules from other
   specifications. Instead, authors have been required to name the rules
   and sources in the specification prose. While this method has served
   authors well, it has hampered machine-readable ABNF efforts for
   services such as syntax highlighting, automatic grammar checking, and
   compiling into target computer languages.

   This document addresses these problems by introducing a reference
   syntax for rules taken from other ABNF grammars, as well as an
   enhanced set of "Core Rules" based on ASCII that are usable without
   needing to be referenced.

2.  Comprehensive Core Rule Update

   This document provides Core Rules that include comprehensive support
   for certain symbols, namely DELETE (DEL) and the C0 controls in
   [ASCII86], which for purposes of this document is equivalent to
   [RFC0020]. The Comprehensive Core Rules are listed in Appendix A as a
   drop-in replacement for the Core Rules of [RFC5234].

3. Reference Syntax

   The purpose of reference syntax is to provide a uniform way to refer
   to rules in other ABNF grammars, without needing to "import",
   "recognize", or "take" all of the rules from those ABNF grammars into
   the subject grammar. The syntax in this section essentially replaces
   the verbiage: "{RULE} is taken from {[RFCXXXX]}" in text that
   describes the ABNF. This verbiage traditionally has appeared in the
   specification prose adjacent to ABNF, in ABNF prose-val productions,
   or in ABNF comments. The varying verbiage has made it difficult for
   both human readers and machine parsers to validate the ABNF. At the
   same time, the presence of such verbiage in the vast majority of
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