The 'application/xhtml+xml' Media Type
Mark A. Baker
Status of this Memo
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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 particular RFC 2854 which registers
This document was prepared by members of the W3C HTML working group
based on the structure, and some of the content, of RFC 2854, the
registration of 'text/html'. Please send comments to
email@example.com, a public mailing list (requiring subscription)
with archives at .
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
Work continues in the HTML WG on XHTML Modularization (see
http://www.w3.org/TR/xhtml-modularization), 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.
As of February 2001, the HTML WG has taken no official position on
what MIME media type should be used to describe XHTML 1.0 or any
other XHTML based language, except in the case where XHTML 1.0
documents satisfy certain additional requirements (see [XHTML1]
section 5.1) and can be described with "text/html" (see [TEXTHTML]).
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. The HTML WG expects to
publish further documentation on this subject, including but not
limited to, information about rules for which documents should and
should not be described with this new media type, and further
information about recognizing XHTML documents.
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
2. Registration of MIME media type application/xhtml+xml
MIME media type name: application
MIME subtype name: xhtml+xml
Required parameters: none
This parameter has identical semantics to the charset parameter
of the "application/xml" media type as specified in [XMLMIME].
See Section 8 of this document.
See Section 4 of this document.
See Section 7 of this document.
XHTML 1.0 [XHTML10] specifies user agent conformance rules that
dictate behaviour that must be followed when dealing with, amoung
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. The HTML WG will be releasing further guidelines about
what documents should and should not be described with this type.
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].
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.
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', reflecting the fact that
no applications currently recognize it. 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]
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.
There are two known file extensions that are currently in use
for XHTML 1.0; ".xht" and ".xhtml".
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 in
section 3. Of course, should the author desire this behaviour,
then the ".xml" extension can be used.
Macintosh File Type code: TEXT
Person & email address to contact for further information:
Intended usage: COMMON
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
For documents labeled as 'application/xhtml+xml', the fragment
identifier notation is exactly that for application/xml, as
specified in [XMLMIME].
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],
5. Recognizing XHTML files
All XHTML files will have the string "
[MIME] Freed, N., and Borenstein, N., "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046, November
[XHTML1] "XHTML 1.0: The Extensible HyperText Markup Language: A
Reformulation of HTML 4 in XML 1.0", W3C Recommendation,
January 2000. Available at .
[XML] "Extensible Markup Language (XML) 1.0", W3C Recommendation,
February 1998. Available at
[TEXTHTML] Connolly, D., Masinter, L., "The 'text/html' Media Type",
RFC 2854, June 2000.
[XMLMIME] Murata, M., St.Laurent, S., Kohn, D., "XML Media Types",
RFC 3023, January 2001.
Appendix A. Revision History (to be removed before publication)
draft-baker-xhtml-media-reg-01: Cleaned up text around "//DTD XHTML"
(thanks to Arjun Ray). Elaborated on the need to keep schema-location
in light of Content-feature and UAPROF. Updated draft-murata-xml
reference to RFC 3023. Added mention of needing to subscribe to
www-html. Added clarification on recommendation against using ".xml".
Changed "schema-location" to "profile", changed description of how it
was used, and added reference to the HTML HEAD parameter of the same