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Network Working Group                                           M. BakerRequest for Comments: 3236                              Planetfred, Inc.Category: Informational                                         P. Stark                                          Ericsson Mobile Communications                                                            January 2002The 'application/xhtml+xml' Media TypeStatus of this Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2002).  All Rights Reserved.Abstract   This document defines the 'application/xhtml+xml' MIME media type for   XHTML based markup languages; it is not intended to obsolete any   previous IETF documents, in particularRFC 2854 which registers   'text/html'.1. Introduction   In 1998, the W3C HTML working group began work on reformulating HTML   in terms of XML 1.0 [XML] and XML Namespaces [XMLNS].  The first part   of that work concluded in January 2000 with the publication of the   XHTML 1.0 Recommendation [XHTML1], the reformulation for HTML 4.01   [HTML401].   Work continues in the Modularization of XHTML Recommendation   [XHTMLM12N], the decomposition of XHTML 1.0 into modules that can be   used to compose new XHTML based languages, plus a framework for   supporting this composition.   This document only registers a new MIME media type,   'application/xhtml+xml'.  It does not define anything more than is   required to perform this registration.Baker & Stark                Informational                      [Page 1]

RFC 3236         The 'application/xhtml+xml' Media Type     January 2002   This document follows the convention set out in [XMLMIME] for the   MIME subtype name; attaching the suffix "+xml" to denote that the   entity being described conforms to the XML syntax as defined in XML   1.0 [XML].   This document was prepared by members of the W3C HTML working group   based on the structure, and some of the content, ofRFC 2854, the   registration of 'text/html'.  Please send comments to www-   html@w3.org, a public mailing list (requiring subscription) with   archives at <http://lists.w3.org/Archives/Public/www-html/>.2. Registration of MIME media type application/xhtml+xml    MIME media type name:      application    MIME subtype name:         xhtml+xml    Required parameters:       none    Optional parameters:      charset         This parameter has identical semantics to the charset parameter         of the "application/xml" media type as specified in [XMLMIME].      profile         SeeSection 8 of this document.   Encoding considerations:      SeeSection 4 of this document.   Security considerations:      SeeSection 7 of this document.   Interoperability considerations:      XHTML 1.0 [XHTML10] specifies user agent conformance rules that      dictate behaviour that must be followed when dealing with, among      other things, unrecognized elements.      With respect to XHTML Modularization [XHTMLMOD] and the existence      of XHTML based languages (referred to as XHTML family members)      that are not XHTML 1.0 conformant languages, it is possible that      'application/xhtml+xml' may be used to describe some of these      documents.  However, it should suffice for now for the purposes of      interoperability that user agents accepting      'application/xhtml+xml' content use the user agent conformance      rules in [XHTML1].Baker & Stark                Informational                      [Page 2]

RFC 3236         The 'application/xhtml+xml' Media Type     January 2002      Although conformant 'application/xhtml+xml' interpreters can      expect that content received is well-formed XML (as defined in      [XML]), it cannot be guaranteed that the content is valid XHTML      (as defined in [XHTML1]).  This is in large part due to the      reasons in the preceding paragraph.   Published specification:      XHTML 1.0 is now defined by W3C Recommendation; the latest      published version is [XHTML1].  It provides for the description of      some types of conformant content as "text/html", but also doesn't      disallow the use with other content types (effectively allowing      for the possibility of this new type).   Applications which use this media type:      Some content authors have already begun hand and tool authoring on      the Web with XHTML 1.0.  However that content is currently      described as "text/html", allowing existing Web browsers to      process it without reconfiguration for a new media type.      There is no experimental, vendor specific, or personal tree      predecessor to 'application/xhtml+xml'.  This new type is being      registered in order to allow for the expected deployment of XHTML      on the World Wide Web, as a first class XML application where      authors can expect that user agents are conformant XML 1.0 [XML]      processors.   Additional information:      Magic number:         There is no single initial byte sequence that is always present         for XHTML files.  However,Section 5 below gives some         guidelines for recognizing XHTML files. See also section 3.1 in         [XMLMIME].      File extension:         There are three known file extensions that are currently in use         for XHTML 1.0; ".xht", ".xhtml", and ".html".         It is not recommended that the ".xml" extension (defined in         [XMLMIME]) be used, as web servers may be configured to         distribute such content as type "text/xml" or         "application/xml".  [XMLMIME] discusses the unreliability of         this approach insection 3.  Of course, should the author         desire this behaviour, then the ".xml" extension can be used.Baker & Stark                Informational                      [Page 3]

RFC 3236         The 'application/xhtml+xml' Media Type     January 2002      Macintosh File Type code: TEXT   Person & email address to contact for further information:      Mark Baker <mark.baker@canada.sun.com>   Intended usage: COMMON   Author/Change controller:      The XHTML specifications are a work product of the World Wide Web      Consortium's HTML Working Group.  The W3C has change control over      these specifications.3. Fragment identifiers   URI references (Uniform Resource Identifiers, see [RFC2396] as   updated by [RFC2732]) may contain additional reference information,   identifying a certain portion of the resource. These URI references   end with a number sign ("#") followed by an identifier for this   portion (called the "fragment identifier"). Interpretation of   fragment identifiers is dependent on the media type of the retrieval   result.   For documents labeled as 'text/html', [RFC2854] specified that the   fragment identifier designates the correspondingly named element,   these were identified by either a unique id attribute or a name   attribute for some elements. For documents described with the   application/xhtml+xml media type, fragment identifiers share the same   syntax and semantics with other XML documents, see [XMLMIME],section5.   At the time of writing, [XMLMIME] does not define syntax and   semantics of fragment identifiers, but refers to "XML Pointer   Language (XPointer)" for a future XML fragment identification   mechanism. The current specification for XPointer is available athttp://www.w3.org/TR/xptr. Until [XMLMIME] gets updated, fragment   identifiers for XHTML documents designate the element with the   corresponding ID attribute value (see [XML]section 3.3.1); any XHTML   element with the "id" attribute.4. Encoding considerations   By virtue of XHTML content being XML, it has the same considerations   when sent as 'application/xhtml+xml' as does XML.  See [XMLMIME],   section 3.2.Baker & Stark                Informational                      [Page 4]

RFC 3236         The 'application/xhtml+xml' Media Type     January 20025. Recognizing XHTML files   All XHTML documents will have the string "<html" near the beginning   of the document.  Some will also begin with an XML declaration which   begins with "<?xml", though that alone does not indicate an XHTML   document.  All conforming XHTML 1.0 documents will include an XML   document type declaration with the root element type 'html'.   XHTML Modularization provides a naming convention by which a public   identifier for an external subset in the document type declaration of   a conforming document will contain the string "//DTD XHTML".  And   while some XHTML based languages require the doctype declaration to   occur within documents of that type, such as XHTML 1.0, or XHTML   Basic (http://www.w3.org/TR/xhtml-basic), it is not the case that all   XHTML based languages will include it.   All XHTML files should also include a declaration of the XHTML   namespace.  This should appear shortly after the string "<html", and   should read 'xmlns="http://www.w3.org/1999/xhtml"'.6. Charset default rules   By virtue of all XHTML content being XML, it has the same   considerations when sent as 'application/xhtml+xml' as does XML.  See   [XMLMIME], section 3.2.7. Security Considerations   The considerations for "text/html" as specified in [TEXTHTML] and and   for 'application/xml' as specified in [XMLMIME], also hold for   'application/xhtml+xml'.   In addition, because of the extensibility features for XHTML as   provided by XHTML Modularization, it is possible that   'application/xhtml+xml' may describe content that has security   implications beyond those described here.  However, if the user agent   follows the user agent conformance rules in [XHTML1], this content   will be ignored.  Only in the case where the user agent recognizes   and processes the additional content, or where further processing of   that content is dispatched to other processors, would security issues   potentially arise.  And in that case, they would fall outside the   domain of this registration document.Baker & Stark                Informational                      [Page 5]

RFC 3236         The 'application/xhtml+xml' Media Type     January 20028. The "profile" optional parameter   This parameter is meant to solve the short-term problem of using MIME   media type based content negotiation (such as that done with the HTTP   "Accept" header) to negotiate for a variety of XHTML based languages.   It is intended to be used only during content negotiation.  It is not   expected that it be used to deliver content, or that origin web   servers have any knowledge of it (though they are welcome to).  It is   primarily targeted for use on the network by proxies in the HTTP   chain that manipulate data formats (such as transcoders).   The parameter is intended to closely match the semantics of the   "profile" attribute of the HEAD element as defined in [HTML401]   (section 7.4.4.3), except it is applied to the document as a whole   rather than just the META elements.  More specifically, the value of   the profile attribute is a URI that can be used as a name to identify   a language.  Though the URI need not be resolved in order to be   useful as a name, it could be a namespace, schema, or a language   specification.   As an example, user agents supporting only XHTML Basic (seehttp://www.w3.org/TR/xhtml-basic) currently have no standard means to   convey their inability to support the additional functionality in   XHTML 1.0 [XHTML1] that is not found in XHTML Basic.  While XHTML   Basic user agent conformance rules (which are identical to XHTML 1.0)   provide some guidance to its user agent implementators for handling   some additional content, the additional content in XHTML 1.0 that is   not part of XHTML Basic is substantial, making those conformance   rules insufficient for practical processing and rendering to the end   user.  There is also the matter of the potentially substantial burden   on the user agent in receiving and parsing this additional content.   The functionality afforded by this parameter can also be achieved   with at least two other more general content description frameworks;   the "Content-features" MIME header described inRFC 2912, and UAPROF   from the WAPforum (seehttp://www.wapforum.org/what/technical.htm).   At this time, choosing one of these solutions would require excluding   the other, as interoperability between the two has not been defined.   For this reason, it is suggested that this parameter be used until   such time as that issue has been addressed.   An example use of this parameter as part of a HTTP GET transaction   would be;      Accept: application/xhtml+xml;        profile="http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd"Baker & Stark                Informational                      [Page 6]

RFC 3236         The 'application/xhtml+xml' Media Type     January 20029. Author's Address   Mark A. Baker   Planetfred, Inc.   44 Byward Market, Suite 240   Ottawa, Ontario, CANADA. K1N 7A2   Phone: +1-613-789-1818   EMail: mbaker@planetfred.com   EMail: distobj@acm.org   Peter Stark   Ericsson Mobile Communications   Phone: +464-619-3000   EMail: Peter.Stark@ecs.ericsson.com10.  References   [HTML401]   Raggett, D., et al., "HTML 4.01 Specification", W3C               Recommendation. Available at               <http://www.w3.org/TR/html401> (or               <http://www.w3.org/TR/1999/REC-html401-19991224>).   [MIME]      Freed, N. and N. Borenstein, "Multipurpose Internet Mail               Extensions (MIME) Part Two: Media Types",RFC 2046,               November 1996.   [URI]       Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform               Resource Identifiers (URI): Generic Syntax",RFC 2396,               August 1998.   [XHTML1]    "XHTML 1.0: The Extensible HyperText Markup Language: A               Reformulation of HTML 4 in XML 1.0", W3C Recommendation.               Available at <http://www.w3.org/TR/xhtml1>.   [XML]       "Extensible Markup Language (XML) 1.0", W3C               Recommendation.  Available at <http://www.w3.org/TR/REC-xml> (or <http://www.w3.org/TR/2000/REC-xml-20001006>).   [TEXTHTML]  Connolly, D. and L. Masinter, "The 'text/html' Media               Type",RFC 2854, June 2000.   [XMLMIME]   Murata, M., St.Laurent, S. and D. Kohn, "XML Media               Types",RFC 3023, January 2001.   [XHTMLM12N] "Modularization of XHTML", W3C Recommendation. Available               at: <http://www.w3.org/TR/xhtml-modularization>Baker & Stark                Informational                      [Page 7]

RFC 3236         The 'application/xhtml+xml' Media Type     January 200211.  Full Copyright Statement   Copyright (C) The Internet Society (2002).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   This document and the information contained herein is provided on an   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING   TASK FORCE DISCLAIMS 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.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Baker & Stark                Informational                      [Page 8]