Network Working Group J. Snell
Internet-Draft September 2006
Expires: March 5, 2007
Atom Bidirectional Extension
draft-snell-atompub-bidi-00.txt
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on March 5, 2007.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This document describes an extension to the Atom format that can be
used to define the base directionality of directionally-neutral
characters contained within an Atom document.
Snell Expires March 5, 2007 [Page 1]
Internet-Draft Atom Bidi September 2006
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Namespace . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Notational Conventions . . . . . . . . . . . . . . . . . . 3
2. The "u:dir" Attribute . . . . . . . . . . . . . . . . . . . . . 3
3. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Normative References . . . . . . . . . . . . . . . . . . . 5
5.2. Informative References . . . . . . . . . . . . . . . . . . 6
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . . . 8
Snell Expires March 5, 2007 [Page 2]
Internet-Draft Atom Bidi September 2006
1. Introduction
This document describes an extension to the Atom format [RFC4287]
that can be 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 XML
elements and attributes described in this specification is
http://purl.org/atompub/bidi
In this document, the namespace prefix "u:" is used for the above
Namespace URI. Note that the choice of namespace prefix is arbitrary
and not semantically significant.
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].
This extension is, like the Atom Syndication Format [RFC4287] itself,
specified using terms from the XML Infoset [W3C.REC-xml-infoset-
20040204]. However, 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.
Some sections of 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 "u:dir" Attribute
The "u: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, "lro" and "rlo" indicating explicit "left-to-right" and
"right-to-left" overrides, or an empty string indicating that no
base-direction is specified. If the "u:dir" attribute is not
specified, the value is assumed to be an empty string. The attribute
can appear anywhere in an Atom document, except where it is
explicitly forbidden.
Snell Expires March 5, 2007 [Page 3]
Internet-Draft Atom Bidi September 2006
dir = attribute u:dir { "ltr" | "rtl" | "lro" | "rlo" | "" }
The direction specified by "u:dir" applies only to elements and
attributes whose values are specified as being "Language-Sensitive"
as defined by Section 2 of [RFC4287]. 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"
xmlns:u="http://purl.org/atompub/bidi" u:dir="rtl">
<title>ٹٺٻ</title>
...
</feed>
If an Atom document contains any right-to-left characters, the
Unicode Bidirectional Algorithm [UNI9] MUST 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.
The "lro" and "rlo" values override the inherent directionality of
characters as defined by [UNICODE]. When used, affected text MUST be
rendered as if preceded by either Unicode character U+202D (left-to-
right override) or U+202E (right-to-left override) and followed by
U+202C (pop directional formatting).
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 "u: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:
Snell Expires March 5, 2007 [Page 4]
Internet-Draft Atom Bidi September 2006
<?xml version="1.0" ?>
<feed xmlns="http://www.w3.org/2005/Atom"
xmlns:u="http://purl.org/atompub/bidi" u: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.
Implementers are reminded that unexpected results could occur when
using both the "u: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,
Snell Expires March 5, 2007 [Page 5]
Internet-Draft Atom Bidi September 2006
<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>.
Appendix A. Acknowledgements
TBD
Snell Expires March 5, 2007 [Page 6]
Internet-Draft Atom Bidi September 2006
Author's Address
James M Snell
Email: jasnell@gmail.com
URI: http://www.snellspace.com
Snell Expires March 5, 2007 [Page 7]
Internet-Draft Atom Bidi September 2006
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2006). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Snell Expires March 5, 2007 [Page 8]
