Network Working Group J. Snell Internet-Draft April 11, 2008 Updates: 4287 (if approved) Intended status: Experimental Expires: October 13, 2008 Atom Bidirectional Attribute draft-snell-atompub-bidi-06.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 October 13, 2008. Copyright Notice Copyright (C) The IETF Trust (2008). Abstract This document adds a new attribute to the Atom Syndication Format used to indicate the base directionality of directionally-neutral characters. Snell Expires October 13, 2008 [Page 1]
Internet-Draft Atom Bidi April 2008 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Namespace . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2. Notational Conventions . . . . . . . . . . . . . . . . . . 3 2. The "dir" Attribute . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Direction Guessing . . . . . . . . . . . . . . . . . . . . 5 3. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.1. Normative References . . . . . . . . . . . . . . . . . . . 6 5.2. Informative References . . . . . . . . . . . . . . . . . . 6 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . . 6 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 7 Intellectual Property and Copyright Statements . . . . . . . . . . 8 Snell Expires October 13, 2008 [Page 2]
Internet-Draft Atom Bidi April 2008 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. Marking bidirectional text using the mechanism defined in this specification is currently considered to be experimental. Implementation and feedback are encouraged. 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 [ISO10646] in an Atom document. 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 a dir attribute is not provided, the value MUST be assumed to be an empty string. The attribute can appear on any element in an Atom document. Snell Expires October 13, 2008 [Page 3]
Internet-Draft Atom Bidi April 2008 atomCommonAttributes = attribute xml:base { atomUri }?, attribute xml:lang { atomLanguageTag }?, attribute dir { "ltr" | "rtl" | "" }?, undefinedAttribute* 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 descendant elements and attributes and may be overridden. Values other than "ltr", "rtl" and "" MUST be ignored and processed as if the dir attribute was not present; Atom processors MUST NOT stop processing or signal an error. The value of the attribute is not case-sensitive. 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 bidirectional text, the Unicode Bidirectional Algorithm [UAX9] 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 or override 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 value is 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: Snell Expires October 13, 2008 [Page 4]
Internet-Draft Atom Bidi April 2008 <?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> 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 using both the "dir" attribute and the Unicode control characters within a single document. 2.1. Direction Guessing In Atom documents that do not contain a "dir" attribute, it is possible to apply heuristics to guess the base directionality of text in the document. Such heuristics can take into consideration the in- scope language context established by the use of the xml:lang attribute or an analysis of the directional properties of the Unicode characters used within the text. Such guessing algorithms can produce reasonably acceptable results in many cases but cannot be guaranteed to produce correct results in every case. For this reason, explicit determination of text direction using the "dir" attribute is preferred over any guessing algorithm. For compatibility with existing Atom documents that rely on direction guessing, user agents MAY perform direction guessing in documents that do not contain a "dir" attribute but they SHOULD NOT do so when an in-scope "dir" attribute is provided. 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 Snell Expires October 13, 2008 [Page 5]
Internet-Draft Atom Bidi April 2008 5.1. Normative References [ISO10646] International Organization for Standardization, "ISO/IEC 10646:2003: Information Technology - Universal Multiple- Octet Coded Character Set (UCS)", December 2003. [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. [UAX9] Davis, M., "Unicode Standard Annex #9: The Bidirectional Algorithm", September 2006. [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 FirstEdition 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>. [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. Snell Expires October 13, 2008 [Page 6]
Internet-Draft Atom Bidi April 2008 Author's Address James M Snell Email: jasnell@gmail.com URI: http://www.snellspace.com Snell Expires October 13, 2008 [Page 7]
Internet-Draft Atom Bidi April 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). 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. 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, THE IETF TRUST 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. Intellectual Property 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. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Snell Expires October 13, 2008 [Page 8]
