INTERNET-DRAFT Mykyta Yevstifeyev
Intended Status: BCP December 8, 2010
Updates: 5234 (if approved)
Expires: June 11, 2011
Augmented Backus-Naur Form (ABNF) Notation for Separated Lists
<draft-yevstifeyev-abnf-separated-lists-02>
Abstract
This document defines Augmented Backus-Naur Form (ABNF) notation for
representing lists separated by any specified character. It updates
RFC 5234.
Status of this Memo
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Copyright and License Notice
Copyright (c) 2010 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
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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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions . . . . . . . . . . . . . . . . . . . . . . . 3
2. Notation Description . . . . . . . . . . . . . . . . . . . . . 4
2.1. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
5. Normative References . . . . . . . . . . . . . . . . . . . . . 6
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Author's Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
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1. Introduction
ABNF does not provide the possibility to express the separated lists
of elements via specific construction. If it is needed (generally for
defining HTTP headers or human-readable forms), the following ABNF
construction is used:
(*LWS element n*m(*LWS separator *LWS element))
It is obvious that this construction is too simplified and bulky.
This document specifies universal ABNF notation for lists, separated
by arbitrary specified characters.
1.1. Conventions
This document uses ABNF notation and core rules defined in RFC 5234
[RFC5234]. The construction in {} is used for expressing arithmetic
expressions. For instance, if a=2, b=3 and c={b-a}, c is 1. In this
case c=1*DIGIT.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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2. Notation Description
The ABNF notation for separated lists is <n>^(<a>)<m>element
indicating at least <n> and at most <m> elements separated by <a> and
OPTIONAL linear-white-spaces.
The ABNF for this construction is:
;if n>=1
n^(a)m element = ( *LWS element n_1*m_1(*LWS a *LWS element)
;if n=0
n^(a)m element = ( *m_1(*LWS element *LWS a) f(element))
n = *DIGIT ;minimum amount of elements, which MUST
;be used
m = *DIGIT ;maximum amount of elements, which MAY be
;used
u = 1*DIGIT ;the number of used elements
n_1 = {n-1}
m_1 = {m-1}
a = VCHAR / SP / HT
f = {(u-(u-1)+1):2} ;will be 0 if no elements are used
;and 1 if at least one element is
;used.
<n> MAY be omitted indicating that any amount of elements not more
than <m> is allowed (including zero).
<m> MAY be omitted indicating that any amount of elements not less
than <n> is allowed (including <n>).
<n> and <m> MAY be omitted indicating that any amount of elements is
allowed (including zero).
2.1. Examples
The section contains a few examples of using the defined
construction.
1^(";")3element indicates the list of elements separated by
semicolons (";") and OPTIONAL linear-white-spaces which consists of
at least 1 and at most 3 elements.
1^(SP)element indicates the list of elements separated by spaces and
OPTIONAL linear-white-spaces which consists of any amount of elements
but not less than 1.
^(",")3element indicates the list of elements separated by commas
(",") and OPTIONAL linear-white-spaces which consists of any amount
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of elements but not more than 3 (including zero).
^(-)element indicates the list of elements separated by hyphens ("-")
and OPTIONAL linear-white-spaces which consists of any amount of
elements (including zero).
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3. Security Considerations
Security issues are not discussed by this document.
4. IANA Considerations
IANA has no actions for this document.
5. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5234] Crocker, D., Ed., and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF", STD 68, RFC 5234, January
2008.
Acknowledgments
Many thanks to (in alphabetical order): Tony Hansen and Barry Leiba
for their weighty input to this document.
Author's Addresses
Mykyta Yevstifeyev
8 Kuzovkov St., flat 25,
Kotovsk, Ukraine
EMail: evnikita2@gmail.com
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