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+Internet Engineering Task Force (IETF)                        P. Kyzivat
+Request for Comments: 7405                                 December 2014
+Updates: 5234
+Category: Standards Track
+ISSN: 2070-1721
+
+
+                 Case-Sensitive String Support in ABNF
+
+Abstract
+
+   This document extends the base definition of ABNF (Augmented Backus-
+   Naur Form) to include a way to specify US-ASCII string literals that
+   are matched in a case-sensitive manner.
+
+Status of This Memo
+
+   This is an Internet Standards Track document.
+
+   This document is a product of the Internet Engineering Task Force
+   (IETF).  It represents the consensus of the IETF community.  It has
+   received public review and has been approved for publication by the
+   Internet Engineering Steering Group (IESG).  Further information on
+   Internet Standards is available in Section 2 of RFC 5741.
+
+   Information about the current status of this document, any errata,
+   and how to provide feedback on it may be obtained at
+   http://www.rfc-editor.org/info/rfc7405.
+
+Copyright Notice
+
+   Copyright (c) 2014 IETF Trust and the persons identified as the
+   document authors.  All rights reserved.
+
+   This document is subject to BCP 78 and the IETF Trust's Legal
+   Provisions Relating to IETF Documents
+   (http://trustee.ietf.org/license-info) in effect on the date of
+   publication of this document.  Please review these documents
+   carefully, as they describe your rights and restrictions with respect
+   to this document.  Code Components extracted from this document must
+   include Simplified BSD License text as described in Section 4.e of
+   the Trust Legal Provisions and are provided without warranty as
+   described in the Simplified BSD License.
+
+
+
+
+
+
+
+
+Kyzivat                      Standards Track                    [Page 1]
+
+RFC 7405          Case-Sensitive String Support in ABNF    December 2014
+
+
+Table of Contents
+
+   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
+   2.  Updates to RFC 5234 . . . . . . . . . . . . . . . . . . . . .   2
+     2.1.  Terminal Values - Literal Text Strings  . . . . . . . . .   3
+     2.2.  ABNF Definition of ABNF - char-val  . . . . . . . . . . .   4
+   3.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
+   4.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
+   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   4
+
+1.  Introduction
+
+   The base definition of ABNF (Augmented Backus-Naur Form) supports US-
+   ASCII string literals.  The matching of these literals is done in a
+   case-insensitive manner.  While this is often the desired behavior,
+   in some situations, case-sensitive matching of string literals is
+   needed.  Literals for case-sensitive matching must be specified using
+   the numeric representation of those characters, which is inconvenient
+   and error prone both to write and read.
+
+   This document extends ABNF to have two different types of US-ASCII
+   string literals.  One type is matched using case-sensitive matching,
+   while the other is matched using case-insensitive matching.  These
+   types are denoted using type prefixes similar to the type prefixes
+   used with numeric values.  If no prefix is used, then case-
+   insensitive matching is used (as is consistent with previous
+   behavior).
+
+   This document is structured as a set of changes to the full ABNF
+   specification [RFC5234].
+
+2.  Updates to RFC 5234
+
+   This document makes changes to two parts of [RFC5234].  The two
+   changes are as follows:
+
+   o  Replace the last half of Section 2.3 of [RFC5234] (beginning with
+      "ABNF permits the specification of literal text strings") with the
+      contents of Section 2.1.
+
+   o  Replace the <char-val> rule in Section 4 of [RFC5234] with the
+      contents of Section 2.2.
+
+
+
+
+
+
+
+
+
+Kyzivat                      Standards Track                    [Page 2]
+
+RFC 7405          Case-Sensitive String Support in ABNF    December 2014
+
+
+2.1.  Terminal Values - Literal Text Strings
+
+   ABNF permits the specification of literal text strings directly,
+   enclosed in quotation marks.  Hence:
+
+         command     =  "command string"
+
+   Literal text strings are interpreted as a concatenated set of
+   printable characters.
+
+   NOTE:
+
+   The character set for these strings is US-ASCII.
+
+   Literal text strings in ABNF may be either case sensitive or case
+   insensitive.  The form of matching used with a literal text string is
+   denoted by a prefix to the quoted string.  The following prefixes are
+   allowed:
+
+         %s          =  case-sensitive
+         %i          =  case-insensitive
+
+   To be consistent with prior implementations of ABNF, having no prefix
+   means that the string is case insensitive and is equivalent to having
+   the "%i" prefix.
+
+   Hence:
+
+         rulename = %i"aBc"
+
+   and:
+
+         rulename = "abc"
+
+   will both match "abc", "Abc", "aBc", "abC", "ABc", "aBC", "AbC", and
+   "ABC".
+
+   In contrast:
+
+         rulename = %s"aBc"
+
+   will match only "aBc" and will not match "abc", "Abc", "abC", "ABc",
+   "aBC", "AbC", or "ABC".
+
+   In the past, the numerical specification of individual characters was
+   used to define a case-sensitive rule.
+
+
+
+
+
+Kyzivat                      Standards Track                    [Page 3]
+
+RFC 7405          Case-Sensitive String Support in ABNF    December 2014
+
+
+   For example:
+
+         rulename    =  %d97 %d98 %d99
+
+   or
+
+         rulename    =  %x61.62.63
+
+   will match only the string that comprises only the lowercase
+   characters, abc.  Using a literal text string with a prefix has a
+   clear readability advantage over the old way.
+
+2.2.  ABNF Definition of ABNF - char-val
+
+         char-val       =  case-insensitive-string /
+                           case-sensitive-string
+
+         case-insensitive-string =
+                           [ "%i" ] quoted-string
+
+         case-sensitive-string =
+                           "%s" quoted-string
+
+         quoted-string  =  DQUOTE *(%x20-21 / %x23-7E) DQUOTE
+                                ; quoted string of SP and VCHAR
+                                ;  without DQUOTE
+
+3.  Security Considerations
+
+   Security is truly believed to be irrelevant to this document.
+
+4.  Normative References
+
+   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
+              Specifications: ABNF", STD 68, RFC 5234, January 2008,
+              <http:/www.rfc-editor.org/info/rfc5234>.
+
+Author's Address
+
+   Paul Kyzivat
+   Massachusetts
+   United States
+
+   EMail: pkyzivat@alum.mit.edu
+
+
+
+
+
+
+
+Kyzivat                      Standards Track                    [Page 4]
+