charset. Following the requirements in section 4.3.3 of [XML], and
optionally applying the mechanism described in Appendix F (non-
normative) of [XML], the XML processor determines the charset of the
XML MIME entity (in this example, UCS-4).
An XML-unaware MIME processor SHOULD make no assumptions about the
charset of the XML MIME entity.
8.12 Text/xml-external-parsed-entity with UTF-8 Charset
Content-type: text/xml-external-parsed-entity; charset="utf-8"
<?xml encoding="utf-8"?>
This is the recommended charset value for use with text/xml-
external-parsed-entity. Since the charset parameter is provided,
MIME and XML processors MUST treat the enclosed entity as UTF-8
encoded.
If sent using a 7-bit transport (e.g., SMTP), the XML MIME entity
MUST use a content-transfer-encoding of either quoted-printable or
base64. For an 8-bit clean transport (e.g., 8BITMIME ESMTP or NNTP),
or a binary clean transport (e.g., HTTP) no content-transfer-encoding
is necessary.
8.13 Application/xml-external-parsed-entity with UTF-16 Charset
Content-type: application/xml-external-parsed-entity;
charset="utf-16"
{BOM}<?xml encoding="utf-16"?>
or
{BOM}<?xml?>
This is a recommended charset value for use with application/xml-
external-parsed-entity. Since the charset parameter is provided,
MIME and XML processors MUST treat the enclosed entity as UTF-16
encoded.
If sent using a 7-bit transport (e.g., SMTP) or an 8-bit clean
transport (e.g., 8BITMIME ESMTP or NNTP), the XML MIME entity MUST be
encoded in quoted-printable or base64. For a binary clean transport
(e.g., HTTP), no content-transfer-encoding is necessary.
8.14 Application/xml-external-parsed-entity with UTF-16BE Charset
Content-type: application/xml-external-parsed-entity;
charset="utf-16be"
<?xml encoding="utf-16be"?>
Since the charset parameter is provided, MIME and XML processors MUST
treat the enclosed entity as UTF-16BE encoded.
8.15 Application/xml-dtd
Content-type: application/xml-dtd; charset="utf-8"
<?xml encoding="utf-8"?>
Charset "utf-8" is a recommended charset value for use with
application/xml-dtd. Since the charset parameter is provided, MIME
and XML processors MUST treat the enclosed entity as UTF-8 encoded.
8.16 Application/mathml+xml
Content-type: application/mathml+xml
<?xml version="1.0" ?>
MathML documents are XML documents whose content describes
mathematical information, as defined by [MathML]. As a format based
on XML, MathML documents SHOULD use the '+xml' suffix convention in
their MIME content-type identifier. However, no content type has yet
been registered for MathML and so this media type should not be used
until such registration has been completed.
8.17 Application/xslt+xml
Content-type: application/xslt+xml
<?xml version="1.0" ?>
Extensible Stylesheet Language (XSLT) documents are XML documents
whose content describes stylesheets for other XML documents, as
defined by [XSLT]. As a format based on XML, XSLT documents SHOULD
use the '+xml' suffix convention in their MIME content-type
identifier. However, no content type has yet been registered for
XSLT and so this media type should not be used until such
registration has been completed.
8.18 Application/rdf+xml
Content-type: application/rdf+xml
<?xml version="1.0" ?>
RDF documents identified using this MIME type are XML documents whose
content describes metadata, as defined by [RDF]. As a format based
on XML, RDF documents SHOULD use the '+xml' suffix convention in
their MIME content-type identifier. However, no content type has yet
been registered for RDF and so this media type should not be used
until such registration has been completed.
8.19 Image/svg+xml
Content-type: image/svg+xml
<?xml version="1.0" ?>
Scalable Vector Graphics (SVG) documents are XML documents whose
content describes graphical information, as defined by [SVG]. As a
format based on XML, SVG documents SHOULD use the '+xml' suffix
convention in their MIME content-type identifier. However, no
content type has yet been registered for SVG and so this media type
should not be used until such registration has been completed.
8.20 INCONSISTENT EXAMPLE: Text/xml with UTF-8 Charset
Content-type: text/xml; charset="utf-8"
<?xml version="1.0" encoding="iso-8859-1"?>
Since the charset parameter is provided in the Content-Type header,
MIME and XML processors MUST treat the enclosed entity as UTF-8
encoded. That is, the "iso-8859-1" encoding MUST be ignored.
Processors generating XML MIME entities MUST NOT label conflicting
charset information between the MIME Content-Type and the XML
declaration.
9. IANA Considerations
As described in Section 7, this document updates the [RFC2048]
registration process for XML-based MIME types.
10. Security Considerations
XML, as a subset of SGML, has all of the same security considerations
as specified in [RFC1874], and likely more, due to its expected
ubiquitous deployment.
To paraphrase section 3 of RFC1874, XML MIME entities contain
information to be parsed and processed by the recipient's XML system.
These entities may contain and such systems may permit explicit
system level commands to be executed while processing the data. To
the extent that an XML system will execute arbitrary command strings,
recipients of XML MIME entities may be a risk. In general, it may be
possible to specify commands that perform unauthorized file
operations or make changes to the display processor's environment
that affect subsequent operations.
In general, any information stored outside of the direct control of
the user -- including CSS style sheets, XSL transformations, entity
declarations, and DTDs -- can be a source of insecurity, by either
obvious or subtle means. For example, a tiny "whiteout attack"
modification made to a "master" style sheet could make words in
critical locations disappear in user documents, without directly
modifying the user document or the stylesheet it references. Thus,
the security of any XML document is vitally dependent on all of the
documents recursively referenced by that document.
The entity lists and DTDs for XHTML 1.0[XHTML], for instance, are
likely to be a commonly used set of information. Many developers
will use and trust them, few of whom will know much about the level
of security on the W3C's servers, or on any similarly trusted
repository.
The simplest attack involves adding declarations that break
validation. Adding extraneous declarations to a list of character
entities can effectively "break the contract" used by documents. A
tiny change that produces a fatal error in a DTD could halt XML
processing on a large scale. Extraneous declarations are fairly
obvious, but more sophisticated tricks, like changing attributes from
being optional to required, can be difficult to track down. Perhaps
the most dangerous option available to crackers is redefining default
values for attributes: e.g., if developers have relied on defaulted
attributes for security, a relatively small change might expose
enormous quantities of information.
Apart from the structural possibilities, another option, "entity
spoofing," can be used to insert text into documents, vandalizing and
perhaps conveying an unintended message. Because XML 1.0 permits
multiple entity declarations, and the first declaration takes
precedence, it's possible to insert malicious content where an entity
is used, such as by inserting the full text of Winnie the Pooh in
every occurrence of —.
Use of the digital signatures work currently underway by the xmldsig
working group may eventually ameliorate the dangers of referencing
external documents not under one's own control.
Use of XML is expected to be varied, and widespread. XML is under
scrutiny by a wide range of communities for use as a common syntax
for community-specific metadata. For example, the Dublin
Core[RFC2413] group is using XML for document metadata, and a new
effort has begun that is considering use of XML for medical
information. Other groups view XML as a mechanism for marshalling
parameters for remote procedure calls. More uses of XML will
undoubtedly arise.
Security considerations will vary by domain of use. For example, XML
medical records will have much more stringent privacy and security
considerations than XML library metadata. Similarly, use of XML as a
parameter marshalling syntax necessitates a case by case security
review.
XML may also have some of the same security concerns as plain text.
Like plain text, XML can contain escape sequences that, when
displayed, have the potential to change the display processor
environment in ways that adversely affect subsequent operations.
Possible effects include, but are not limited to, locking the
keyboard, changing display parameters so subsequent displayed text is
unreadable, or even changing display parameters to deliberately
obscure or distort subsequent displayed material so that its meaning
is lost or altered. Display processors SHOULD either filter such
material from displayed text or else make sure to reset all important
settings after a given display operation is complete.
Some terminal devices have keys whose output, when pressed, can be
changed by sending the display processor a character sequence. If
this is possible the display of a text object containing such
character sequences could reprogram keys to perform some illicit or
dangerous action when the key is subsequently pressed by the user.
In some cases not only can keys be programmed, they can be triggered
remotely, making it possible for a text display operation to directly
perform some unwanted action. As such, the ability to program keys
SHOULD be blocked either by filtering or by disabling the ability to
program keys entirely.
Note that it is also possible to construct XML documents that make
use of what XML terms "entity references" (using the XML meaning of
the term "entity" as described in Section 2), to construct repeated
expansions of text. Recursive expansions are prohibited by [XML] and
XML processors are required to detect them. However, even non-
recursive expansions may cause problems with the finite computing
resources of computers, if they are performed many times.
References
[ASCII] "US-ASCII. Coded Character Set -- 7-Bit American Standard
Code for Information Interchange", ANSI X3.4-1986, 1986.
[CSS] Bos, B., Lie, H.W., Lilley, C. and I. Jacobs, "Cascading
Style Sheets, level 2 (CSS2) Specification", World Wide
Web Consortium Recommendation REC-CSS2, May 1998,
<http://www.w3.org/TR/REC-CSS2/>.
[ISO8859] "ISO-8859. International Standard -- Information
Processing -- 8-bit Single-Byte Coded Graphic Character
Sets -- Part 1: Latin alphabet No. 1, ISO-8859-1:1987",
1987.
[MathML] Ion, P. and R. Miner, "Mathematical Markup Language
(MathML) 1.01", World Wide Web Consortium Recommendation
REC-MathML, July 1999, <http://www.w3.org/TR/REC-MathML/>.
[PNG] Boutell, T., "PNG (Portable Network Graphics)
Specification", World Wide Web Consortium Recommendation
REC-png, October 1996, <http://www.w3.org/TR/REC-png>.
[RDF] Lassila, O. and R.R. Swick, "Resource Description
Framework (RDF) Model and Syntax Specification", World
Wide Web Consortium Recommendation REC-rdf-syntax,
February 1999, <http://www.w3.org/TR/REC-rdf-syntax/>.
[RFC0821] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC
821, August 1982.
[RFC0977] Kantor, B. and P. Lapsley, "Network News Transfer
Protocol", RFC977, February 1986.
[RFC1557] Choi, U., Chon, K. and H. Park, "Korean Character Encoding
for Internet Messages", RFC1557, December 1993.
[RFC1652] Klensin, J., Freed, N., Rose, M., Stefferud, E. and D.
Crocker, "SMTP Service Extension for 8bit-MIMEtransport",
RFC1652, July 1994.
[RFC1874] Levinson, E., "SGML Media Types", RFC1874, December 1995.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC2045, November 1996.
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC2046,
November 1996.
[RFC2048] Freed, N., Klensin, J. and J. Postel, "Multipurpose
Internet Mail Extensions (MIME) Part Four: Registration
Procedures", RFC2048, November 1996.
[RFC2060] Crispin, M., "Internet Message Access Protocol - Version
4rev1", RFC2060, December 1996.
[RFC2077] Nelson, S., Parks, C. and Mitra, "The Model Primary
Content Type for Multipurpose Internet Mail Extensions",
RFC2077, January 1997.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC2119, March 1997.
[RFC2130] Weider, C., Preston, C., Simonsen, K., Alvestrand, H.,
Atkinson, R., Crispin, M. and P. Svanberg, "The Report of
the IAB Character Set Workshop held 29 February - 1 March,
1996", RFC2130, April 1997.
[RFC2279] Yergeau, F., "UTF-8, a transformation format of ISO
10646", RFC2279, January 1998.
[RFC2376] Whitehead, E. and M. Murata, "XML Media Types", RFC2376,
July 1998.
[RFC2396] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax.", RFC2396,
August 1998.
[RFC2413] Weibel, S., Kunze, J., Lagoze, C. and M. Wolf, "Dublin
Core Metadata for Resource Discovery", RFC2413, September
1998.
[RFC2445] Dawson, F. and D. Stenerson, "Internet Calendaring and
Scheduling Core Object Specification (iCalendar)", RFC
2445, November 1998.
[RFC2518] Goland, Y., Whitehead, E., Faizi, A., Carter, S. and D.
Jensen, "HTTP Extensions for Distributed Authoring --
WEBDAV", RFC2518, February 1999.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Nielsen, H.,
Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC2616, June 1999.
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC2629,
June 1999.
[RFC2703] Klyne, G., "Protocol-independent Content Negotiation
Framework", RFC2703, September 1999.
[RFC2781] Hoffman, P. and F. Yergeau, "UTF-16, an encoding of ISO
10646", RFC2781, Februrary 2000.
[RFC2801] Burdett, D., "Internet Open Trading Protocol - IOTP
Version 1.0", RFC2801, April 2000.
[SGML] International Standard Organization, "Information
Processing -- Text and Office Systems -- Standard
Generalized Markup Language (SGML)", ISO 8879, October
1986.
[SVG] Ferraiolo, J., "Scalable Vector Graphics (SVG)", World
Wide Web Consortium Candidate Recommendation SVG, November
2000, <http://www.w3.org/TR/SVG>.
[XHTML] Pemberton, S. and et al, "XHTML 1.0: The Extensible
HyperText Markup Language", World Wide Web Consortium
Recommendation xhtml1, January 2000,
<http://www.w3.org/TR/xhtml1>.
[XML] Bray, T., Paoli, J., Sperberg-McQueen, C.M. and E. Maler,
"Extensible Markup Language (XML) 1.0 (Second Edition)",
World Wide Web Consortium Recommendation REC-xml, October
2000, <http://www.w3.org/TR/REC-xml>.
[XSLT] Clark, J., "XSL Transformations (XSLT) Version 1.0", World
Wide Web Consortium Recommendation xslt, November 1999,
<http://www.w3.org/TR/xslt>.
Authors' Addresses
MURATA Makoto (FAMILY Given)
IBM Tokyo Research Laboratory
1623-14, Shimotsuruma
Yamato-shi, Kanagawa-ken 242-8502
Japan
Phone: +81-46-215-4678
EMail: mmurata@trl.ibm.co.jp
Simon St.Laurent
simonstl.com
1259 Dryden Road
Ithaca, New York 14850
USA
EMail: simonstl@simonstl.com
URI: http://www.simonstl.com/
Dan Kohn
Skymoon Ventures
3045 Park Boulevard
Palo Alto, California 94306
USA
Phone: +1-650-327-2600
EMail: dan@dankohn.com
URI: http://www.dankohn.com/
Appendix A. Why Use the '+xml' Suffix for XML-Based MIME Types?
Although the use of a suffix was not considered as part of the
original MIME architecture, this choice is considered to provide the
most functionality with the least potential for interoperability
problems or lack of future extensibility. The alternatives to the
'+xml' suffix and the reason for its selection are described below.
A.1 Why not just use text/xml or application/xml and let the XML
processor dispatch to the correct application based on the
referenced DTD?
text/xml and application/xml remain useful in many situations,
especially for document-oriented applications that involve combining
XML with a stylesheet in order to present the data. However, XML is
also used to define entirely new data types, and an XML-based format
such as image/svg+xml fits the definition of a MIME media type
exactly as well as image/png[PNG] does. (Note that image/svg+xml is
not yet registered.) Although extra functionality is available for
MIME processors that are also XML processors, XML-based media types
-- even when treated as opaque, non-XML media types -- are just as
useful as any other media type and should be treated as such.
Since MIME dispatchers work off of the MIME type, use of text/xml or
application/xml to label discrete media types will hinder correct
dispatching and general interoperability. Finally, many XML
documents use neither DTDs nor namespaces, yet are perfectly legal
XML.
A.2 Why not create a new subtree (e.g., image/xml.svg) to represent XML
MIME types?
The subtree under which a media type is registered -- IETF, vendor
(*/vnd.*), or personal (*/prs.*); see [RFC2048] for details -- is
completely orthogonal from whether the media type uses XML syntax or
not. The suffix approach allows XML document types to be identified
within any subtree. The vendor subtree, for example, is likely to
include a large number of XML-based document types. By using a
suffix, rather than setting up a separate subtree, those types may
remain in the same location in the tree of MIME types that they would
have occupied had they not been based on XML.
A.3 Why not create a new top-level MIME type for XML-based media types?
The top-level MIME type (e.g., model/*[RFC2077]) determines what kind
of content the type is, not what syntax it uses. For example, agents
using image/* to signal acceptance of any image format should
certainly be given access to media type image/svg+xml, which is in
all respects a standard image subtype. It just happens to use XML to
describe its syntax. The two aspects of the media type are
completely orthogonal.
XML-based data types will most likely be registered in ALL top-level
categories. Potential, though currently unregistered, examples could
include application/mathml+xml[MathML] and image/svg+xml[SVG].
A.4 Why not just have the MIME processor 'sniff' the content to
determine whether it is XML?
Rather than explicitly labeling XML-based media types, the processor
could look inside each type and see whether or not it is XML. The
processor could also cache a list of XML-based media types.
Although this method might work acceptably for some mail
applications, it would fail completely in many other uses of MIME.
For instance, an XML-based web crawler would have no way of
determining whether a file is XML except to fetch it and check. The
same issue applies in some IMAP4[RFC2060] mail applications, where
the client first fetches the MIME type as part of the message
structure and then decides whether to fetch the MIME entity.
Requiring these fetches just to determine whether the MIME type is
XML could have significant bandwidth and latency disadvantages in
many situations.
Sniffing XML also isn't as simple as it might seem. DOCTYPE
declarations aren't required, and they can appear fairly deep into a
document under certain unpreventable circumstances. (E.g., the XML
declaration, comments, and processing instructions can occupy space
before the DOCTYPE declaration.) Even sniffing the DOCTYPE isn't
completely reliable, thanks to a variety of issues involving default
values for namespaces within external DTDs and overrides inside the
internal DTD. Finally, the variety in potential character encodings
(something XML provides tools to deal with), also makes reliable
sniffing less likely.
A.5 Why not use a MIME parameter to specify that a media type uses XML
syntax?
For example, one could use "Content-Type: application/iotp;
alternate-type=text/xml" or "Content-Type: application/iotp;
syntax=xml".
Section 5 of [RFC2045] says that "Parameters are modifiers of the
media subtype, and as such do not fundamentally affect the nature of
the content". However, all XML-based media types are by their nature
always XML. Parameters, as they have been defined in the MIME
architecture, are never invariant across all instantiations of a
media type.
More practically, very few if any MIME dispatchers and other MIME
agents support dispatching off of a parameter. While MIME agents on
the receiving side will need to be updated in either case to support
(or fall back to) generic XML processing, it has been suggested that
it is easier to implement this functionality when acting off of the
media type rather than a parameter. More important, sending agents
require no update to properly tag an image as "image/svg+xml", but
few if any sending agents currently support always tagging certain
content types with a parameter.
A.6 How about labeling with parameters in the other direction (e.g.,
application/xml; Content-Feature=iotp)?
This proposal fails under the simplest case, of a user with neither
knowledge of XML nor an XML-capable MIME dispatcher. In that case,
the user's MIME dispatcher is likely to dispatch the content to an
XML processing application when the correct default behavior should
be to dispatch the content to the application responsible for the
content type (e.g., an ecommerce engine for
application/iotp+xml[RFC2801], once this media type is registered).
Note that even if the user had already installed the appropriate
application (e.g., the ecommerce engine), and that installation had
updated the MIME registry, many operating system level MIME
registries such as .mailcap in Unix and HKEY_CLASSES_ROOT in Windows
do not currently support dispatching off a parameter, and cannot
easily be upgraded to do so. And, even if the operating system were
upgraded to support this, each MIME dispatcher would also separately
need to be upgraded.
A.7 How about a new superclass MIME parameter that is defined to apply
to all MIME types (e.g., Content-Type: application/iotp;
$superclass=xml)?
This combines the problems of Appendix A.5 and Appendix A.6.
If the sender attaches an image/svg+xml file to a message and
includes the instructions "Please copy the French text on the road
sign", someone with an XML-aware MIME client and an XML browser but
no support for SVG can still probably open the file and copy the
text. By contrast, with superclasses, the sender must add superclass
support to her existing mailer AND the receiver must add superclass
support to his before this transaction can work correctly.
If the receiver comes to rely on the superclass tag being present and
applications are deployed relying on that tag (as always seems to
happen), then only upgraded senders will be able to interoperate with
those receiving applications.
A.8 What about adding a new parameter to the Content-Disposition header
or creating a new Content-Structure header to indicate XML syntax?
This has nearly identical problems to Appendix A.7, in that it
requires both senders and receivers to be upgraded, and few if any
operating systems and MIME dispatchers support working off of
anything other than the MIME type.
A.9 How about a new Alternative-Content-Type header?
This is better than Appendix A.8, in that no extra functionality
needs to be added to a MIME registry to support dispatching of
information other than standard content types. However, it still
requires both sender and receiver to be upgraded, and it will also
fail in many cases (e.g., web hosting to an outsourced server), where
the user can set MIME types (often through implicit mapping to file
extensions), but has no way of adding arbitrary HTTP headers.
A.10 How about using a conneg tag instead (e.g., accept-features:
(syntax=xml))?
When the conneg protocol is fully defined, this may potentially be a
reasonable thing to do. But given the limited current state of
conneg[RFC2703] development, it is not a credible replacement for a
MIME-based solution.
A.11 How about a third-level content-type, such as text/xml/rdf?
MIME explicitly defines two levels of content type, the top-level for
the kind of content and the second-level for the specific media type.
[RFC2048] extends this in an interoperable way by using prefixes to
specify separate trees for IETF, vendor, and personal registrations.
This specification also extends the two-level type by using the '
+xml' suffix. In both cases, processors that are unaware of these
later specifications treat them as opaque and continue to
interoperate. By contrast, adding a third-level type would break the
current MIME architecture and cause numerous interoperability
failures.
A.12 Why use the plus ('+') character for the suffix '+xml'?
As specified in Section 5.1 of [RFC2045], a tspecial can't be used:
tspecials :=
"(" / ")" / "<" / ">" / "@" /
"," / ";" / ":" / "\" / <">
"/" / "[" / "]" / "?" / "="
It was thought that "." would not be a good choice since it is
already used as an additional hierarchy delimiter. Also, "*" has a
common wildcard meaning, and "-" and "_" are common word separators
and easily confused. The characters %'`#& are frequently used for
quoting or comments and so are not ideal.
That leaves: ~!$^+{}|
Note that "-" is used heavily in the current registry. "$" and "_"
are used once each. The others are currently unused.
It was thought that '+' expressed the semantics that a MIME type can
be treated (for example) as both scalable vector graphics AND ALSO as
XML; it is both simultaneously.
A.13 What is the semantic difference between application/foo and
application/foo+xml?
MIME processors that are unaware of XML will treat the '+xml' suffix
as completely opaque, so it is essential that no extra semantics be
assigned to its presence. Therefore, application/foo and
application/foo+xml SHOULD be treated as completely independent media
types. Although, for example, text/calendar+xml could be an XML
version of text/calendar[RFC2445], it is possible that this
(hypothetical) new media type would include new semantics as well as
new syntax, and in any case, there would be many applications that
support text/calendar but had not yet been upgraded to support
text/calendar+xml.
A.14 What happens when an even better markup language (e.g., EBML) is
defined, or a new category of data?
In the ten years that MIME has existed, XML is the first generic data
format that has seemed to justify special treatment, so it is hoped
that no further suffixes will be necessary. However, if some are
later defined, and these documents were also XML, they would need to
specify that the '+xml' suffix is always the outermost suffix (e.g.,
application/foo+ebml+xml not application/foo+xml+ebml). If they were
not XML, then they would use a regular suffix (e.g.,
application/foo+ebml).
A.15 Why must I use the '+xml' suffix for my new XML-based media type?
You don't have to, but unless you have a good reason to explicitly
disallow generic XML processing, you should use the suffix so as not
to curtail the options of future users and developers.
Whether the inventors of a media type, today, design it for dispatch
to generic XML processing machinery (and most won't) is not the
critical issue. The core notion is that the knowledge that some
media type happens to use XML syntax opens the door to unanticipated
kinds of processing beyond those envisioned by its inventors, and on
this basis identifying such encoding is a good and useful thing.
Developers of new media types are often tightly focused on a
particular type of processing that meets current needs. But there is
no need to rule out generic processing as well, which could make your
media type more valuable over time. It is believed that registering
with the '+xml' suffix will cause no interoperability problems
whatsoever, while it may enable significant new functionality and
interoperability now and in the future. So, the conservative
approach is to include the '+xml' suffix.
Appendix B. Changes from RFC2376
There are numerous and significant differences between this
specification and [RFC2376], which it obsoletes. This appendix
summarizes the major differences only.
First, text/xml-external-parsed-entity and application/xml-external-
parsed-entity are added as media types for external parsed entities,
and text/xml and application/xml are now prohibited.
Second, application/xml-dtd is added as a media type for external DTD
subsets and external parameter entities, and text/xml and
application/xml are now prohibited.
Third, "utf-16le" and "utf-16be" are added. RFC2781 has introduced
these BOM-less variations of the UTF-16 family.
Fourth, a naming convention ('+xml') for XML-based media types has
been added, which also updates [RFC2048] as described in Section 7.
By following this convention, an XML-based media type can be easily
recognized as such.
Appendix C. Acknowledgements
This document reflects the input of numerous participants to the
ietf-xml-mime@imc.org mailing list, though any errors are the
responsibility of the authors. Special thanks to:
Mark Baker, James Clark, Dan Connolly, Martin Duerst, Ned Freed,
Yaron Goland, Rick Jelliffe, Larry Masinter, David Megginson, Keith
Moore, Chris Newman, Gavin Nicol, Marshall Rose, Jim Whitehead and
participants of the XML activity at the W3C.
Full Copyright Statement
Copyright (C) The Internet Society (2001). All Rights Reserved.
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