Network Working Group J. Snell
Internet-Draft December 5, 2006
Expires: June 8, 2007
Atom Bidirectional Attribute
draft-snell-atompub-bidi-02.txt
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Copyright (C) The IETF Trust (2006).
Abstract
This document adds a new attribute to the Atom Syndication Format
used to indicate the base directionality of directionally-neutral
characters.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Namespace . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Notational Conventions . . . . . . . . . . . . . . . . . . 3
2. The "dir" Attribute . . . . . . . . . . . . . . . . . . . . . . 3
3. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Normative References . . . . . . . . . . . . . . . . . . . 5
5.2. Informative References . . . . . . . . . . . . . . . . . . 5
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . . . 8
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1. Introduction
This document updates the Atom Syndication Format [RFC4287] by adding
a new 'dir' attribute used to define the base directionality of
directionally-neutral characters contained within an Atom document.
1.1. Namespace
The XML Namespaces URI [W3C.REC-xml-names-19990114] for the Atom
Syndication Format [RFC4287] is:
http://www.w3.org/2005/Atom
1.2. Notational Conventions
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 BCP 14, [RFC2119].
The Atom Syndication Format [RFC4287] is specified using terms from
the XML Infoset [W3C.REC-xml-infoset-20040204]. This specification
uses a shorthand form for two commons terms: The phrase "Information
Item" is omitted when naming Element and Attribute Information Items.
Therefore, when this specification uses the term "element," it is
referring to an Element Information Item in Infoset terms. Likewise,
when it uses the term "attribute," it is referring to an Attribute
Information Item.
Portions this specification are illustrated with fragments of a non-
normative RELAX NG Compact schema [RELAXNG]. However, the text of
this specification provides the sole definition of conformance.
2. The "dir" Attribute
The "dir" attribute specifies the base direction of directionally-
neutral text [UNICODE]. Possible values for the attribute are "ltr"
and "rtl" indicating "left-to-right" and "right-to-left"
respectively, or an empty string indicating that no base-direction is
specified. If the "dir" attribute is not specified, the value is
assumed to be an empty string. The attribute can appear on any
element in an Atom document.
atomCommonAttributes =
attribute xml:base { atomUri }?,
attribute xml:lang { atomLanguageTag }?,
attribute dir { "ltr" | "rtl" | "" }?,
undefinedAttribute*
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The direction specified by "dir" applies to elements and attributes
whose values are specified as being "Language-Sensitive" as defined
by Section 2 of [RFC4287]. The direction specified by the attribute
is inherited by descendent elements and may be overridden.
Example atom:feed with right-to-left directionality
<?xml version="1.0" ?>
<feed xmlns="http://www.w3.org/2005/Atom" dir="rtl">
<title>ٹٺٻ</title>
...
</feed>
If an Atom document contains any right-to-left characters, the
Unicode Bidirectional Algorithm [UNI9] SHOULD be used to render that
text. Because consumers of Atom documents vary broadly in the way
they display text, the "ltr" and "rtl" values do not necessarily open
an additional level of embedding with respect to the bidirectional
algorithm. Consuming applications that render bidirectional text are
responsible for determining the appropriate level of embedding. If
the dir attribute value is "rtl", Atom processors that display
affected text MAY choose to right-align that text as per the rules
described in Section 8 of [W3C.REC-html401-19991224].
When Atom Text Constructs or the atom:content elements contain
bidirectional text and the type attribute is set to either "html" or
"xhtml", the bidirectional markup mechanisms specific to each format
SHOULD be used. The value of the "dir" attribute does define the
base directionality of Language-Sensitive text within Text Constructs
and atom:content elements regardless of the value of the type
attribute.
Example atom:feed with bidirectional XHTML:
<?xml version="1.0" ?>
<feed xmlns="http://www.w3.org/2005/Atom" dir="rtl">
<title type="xhtml">
<div xmlns="http://www.w3.org/1999/xhtml">
<p dir="rtl">ٹٺٻ</p>
</div>
</title>
...
</feed>
The Unicode bidirectional control characters MAY also be used within
attributes and element values to indicate the directionality of text
or to modify the default operation of the Bidirectional Algorithm.
Implementers are reminded that unexpected results could occur when
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using both the "dir" attribute and the Unicode control characters
within a single document.
3. Security Considerations
The security considerations discussed in [RFC4287] Section 8 apply.
4. IANA Considerations
No IANA actions are required by this document.
5. References
5.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4287] Nottingham, M., Ed. and R. Sayre, Ed., "The Atom
Syndication Format", RFC 4287, December 2005.
[UNI9] Davis, M., "The Bidirectional Algorithm", March 2004.
[UNICODE] International Organization for Standardization, "ISO/IEC
10646:2003: Information Technology - Universal Multiple-
Octet Coded Character Set (UCS)", December 2003.
[W3C.REC-xml-infoset-20040204]
Cowan, J. and R. Tobin, "XML Information Set (Second
Edition)", World Wide Web Consortium Recommendation REC-
xml-infoset-20040204, February 2004,
<http://www.w3.org/TR/2004/REC-xml-infoset-20040204>.
[W3C.REC-xml-names-19990114]
Layman, A., Bray, T., and D. Hollander, "Namespaces in
XML", World Wide Web Consortium Recommendation REC-xml-
names-19990114, January 1999,
<http://www.w3.org/TR/1999/REC-xml-names-19990114>.
5.2. Informative References
[RELAXNG] Clark, J., "RELAX NG Compact Syntax", December 2001, <http
://www.oasis-open.org/committees/relax-ng/
compact-20021121.html>.
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[W3C.REC-html401-19991224]
Jacobs, I., Raggett, D., and A. Hors, "HTML 4.01
Specification", World Wide Web Consortium
Recommendation REC-html401-19991224, December 1999,
<http://www.w3.org/TR/1999/REC-html401-19991224>.
Appendix A. Acknowledgements
The author gratefully acknowledges the feedback from the Atom
Publishing Format and Protocol Working Group.
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Author's Address
James M Snell
Email: jasnell@gmail.com
URI: http://www.snellspace.com
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