WDIFF

draft-murata-xml-02.txt --> draft-murata-xml-03.txt

Network Working Group
Internet-Draft M. Murata
Expires: May 31, 2000 Fuji Xerox Information Systems
Internet-Draft S. St.Laurent
December 1999
Expires: September 30, 2000 D. Kohn
April 2000

XML Media Types
draft-murata-xml-02.txt
draft-murata-xml-03.txt

Status of this Memo

This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.

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
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Internet-Drafts are draft documents valid for a maximum of six
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The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
http://www.ietf.org/ietf/1id-abstracts.txt.

The list of Internet-Draft Shadow Directories can be accessed at
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This Internet-Draft will expire on May 31, September 30, 2000.

Abstract

This document proposes standardizes five new media types, text/xml,
application/xml, text/xml-external-parsed-entity,
application/xml-external-parsed-entity, and application/xml-dtd, for
use in exchanging network entities which are conforming related to the
Extensible Markup Language (XML). This document also proposes standardizes a
convention (using the suffix '|xml') for naming media subtypes types outside
of these five subtypes types when those
subtypes media types represent XML entities.
XML MIME entities are currently exchanged via the HyperText Transfer
Protocol on the World Wide Web, are an integral part of the WebDAV
protocol for remote web authoring, and are expected to have utility
in many domains.

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[This document is intended to be a standards-track replacement for
RFC 2376. It could also be specified as updating RFC 2048.]

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 4
2. Editor's Notes . . . . . . . . . . . . . . . . . . . . . . . 4
2. 5
3. Notational Conventions . . . . . . . . . . . . . . . . . . . 5
3. 6
4. XML Media Types . . . . . . . . . . . . . . . . . . . . . . 6
3.1 7
4.1 Text/xml Registration . . . . . . . . . . . . . . . . . . . 7
3.2 8
4.2 Application/xml Registration . . . . . . . . . . . . . . . . 9
3.3 text/xml-external-parsed-entity 11
4.3 Text/xml-external-parsed-entity Registration . . . . . . . . 11
3.4 application/xml-external-parsed-entity 12
4.4 Application/xml-external-parsed-entity Registration . . . . 13
3.5
4.5 Application/xml-dtd Registration . . . . . . . . . . . . . . 14
4. Security Considerations . . .
4.6 Summary . . . . . . . . . . . . . . . 16
5. The Byte Order Mark (BOM) and Conversions to/from UTF-16 . . 18
6. A naming convention for XML-based media types . . . . . . . 19
7. Examples . . 15
4.7 Referencing . . . . . . . . . . . . . . . . . . . . . . . . 21
7.1 text/xml with UTF-8 16
5. The Byte Order Mark (BOM) and Conversions to/from the UTF-16
Charset . . . . . . . . . . . . . . . . 21
7.2 text/xml with UTF-16 Charset . . . . . . . . . . . . . . . . 21
7.3 text/xml with ISO-2022-KR Charset 17
6. Fragment Identifiers . . . . . . . . . . . . . 21
7.4 text/xml with Omitted Charset . . . . . . . 18
7. The Base URI . . . . . . . . 22
7.5 application/xml with UTF-16 Charset . . . . . . . . . . . . 22
7.6 application/xml with ISO-2022-KR Charset . . . . 19
8. A Naming Convention for XML-Based Media Types . . . . . . 22
7.7 application/xml with Omitted Charset and UTF-16 XML MIME
entity . 20
9. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 23
7.8 application/xml
9.1 Text/xml with Omitted Charset and UTF-8 Entity Charset . . . 23
7.9 application/xml with Omitted Charset and Internal Encoding
Declaration . . . . . . . . . . . . . 23
9.2 Text/xml with UTF-16 Charset . . . . . . . . . . . 23
7.10 text/xml-external-parsed-entity with UTF-8 Charset . . . . . 24
7.11 application/xml-external-parsed-entity 23
9.3 Text/xml with UTF-16 UTF-16BE Charset . 24
7.12 application/xml-dtd . . . . . . . . . . . . . . 24
9.4 Text/xml with ISO-2022-KR Charset . . . . . . 24
7.13 application/mathml-xml . . . . . . . 24
9.5 Text/xml with Omitted Charset . . . . . . . . . . . . 25
7.14 application/XSLT-xml . . . 24
9.6 Application/xml with UTF-16 Charset . . . . . . . . . . . . 24
9.7 Application/xml with UTF-16BE Charset . . . . . 25
7.15 application/rdf-xml . . . . . . 25
9.8 Application/xml with ISO-2022-KR Charset . . . . . . . . . . 25
9.9 Application/xml with Omitted Charset and UTF-16 XML MIME
Entity . . . . 25
7.16 image/svg-xml . . . . . . . . . . . . . . . . . . . . . . . 25
8. Revision History . . .
9.10 Application/xml with Omitted Charset and UTF-8 Entity . . . 26
9.11 Application/xml with Omitted Charset and Internal Encoding
Declaration . . . . . . . . . . . . . . . . 26
References . . . . . . . . 26
9.12 Text/xml-external-parsed-entity with UTF-8 Charset . . . . . 26
9.13 Application/xml-external-parsed-entity with UTF-16 Charset . 27
9.14 Application/xml-external-parsed-entity with UTF-16BE Charset 27
9.15 Application/xml-dtd . . . . . . . . . . . . . . . . . . . . 27
Authors' Addresses
9.16 Application/mathml|xml . . . . . . . . . . . . . . . . . . . 28
9.17 Application/xslt|xml . . . . . . . . . . . . . . . . . . . . 28
A. Acknowledgement
9.18 Application/rdf|xml . . . . . . . . . . . . . . . . . . . . 28
9.19 Image/svg|xml . . 30
Full Copyright Statement . . . . . . . . . . . . . . . . . . 31

, . . . 28
10. Security Considerations . . . . . . . . . . . . . . . . . . 29
References . . . . . . . . . . . . . . . . . . . . . . . . . 32
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 34
A. Why Use the '|xml' Suffix for XML-Based MIME Types? . . . . 36
A.1 Why not just use text/xml or application/xml and let the XML
processor dispatch to the correct application based on the

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1. Introduction

The World Wide Web Consortium (W3C)[20] has issued Extensible
Markup Language (XML), version 1[10]. To enable the exchange of XML
network entities, this document proposes five April 2000

referenced DTD? . . . . . . . . . . . . . . . . . . . . . . 36
A.2 Why not create a new media types,
text/xml, application/xml, text/xml-external-parsed-entity,
application/xml-external-parsed-entity, and application/xml-dtd as
well as subtree (e.g., image/xml.svg) to
represent XML MIME types? . . . . . . . . . . . . . . . . . 36
A.3 Why not create a naming convention new top-level MIME type for identifying XML-based MIME media
types.

XML entities are currently exchanged on the World Wide Web, and XML
is also used for property values and parameter marshalling by
types? . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
A.4 Why not just have the
WebDAV protocol for remote web authoring. Thus, there MIME processor 'sniff' the content to
determine whether it is XML? . . . . . . . . . . . . . . . . 37
A.5 Why not use a need for MIME parameter to specify that a media type to properly label the exchange of
uses XML network entities.
(Note that, as sometimes happens between two communities, both syntax? . . . . . . . . . . . . . . . . . . . . . . 37
A.6 How about labeling with parameters in the other direction
(e.g., application/xml; Content-Feature=iotp)? . . . . . . . 38
A.7 How about a new superclass MIME
and XML have parameter that is defined to
apply to all MIME types (e.g., Content-Type:
application/iotp; $superclass=xml)? . . . . . . . . . . . . 38
A.8 What about adding a new parameter to the term entity, with different meanings.)

Although Content-Disposition
header or creating a new Content-Structure header to
indicate XML is syntax? . . . . . . . . . . . . . . . . . . . . 39
A.9 How about a subset of the Standard Generalized Markup Language
(SGML) ISO 8879[1], and currently new Alternative-Content-Type header? . . . . . . 39
A.10 How about using a conneg tag instead (e.g., accept-features:
(syntax=xml))? . . . . . . . . . . . . . . . . . . . . . . . 39
A.11 How about a third-level content-type, such as text/xml/rdf? 39
A.12 What is assigned the media types
text/sgml semantic difference between application/foo and application/sgml,
application/foo|xml? . . . . . . . . . . . . . . . . . . . . 39
A.13 What happens when an even better markup language (e.g.,
EBML) is defined, or a new category of data? . . . . . . . . 40
A.14 Why must I use the '|xml' suffix for my new XML-based media
type? . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
B. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 41
C. Revision History . . . . . . . . . . . . . . . . . . . . . . 42
Full Copyright Statement . . . . . . . . . . . . . . . . . . 43

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1. Introduction

The World Wide Web Consortium has issued Extensible Markup Language
(XML), version 1.0[XML]. To enable the exchange of XML network
entities, this document standardizes five new media types, text/xml,
application/xml, text/xml-external-parsed-entity,
application/xml-external-parsed-entity, and application/xml-dtd as
well as a naming convention for identifying XML-based MIME media
types.

XML entities are currently exchanged on the World Wide Web, and XML
is also used for property values and parameter marshalling by the
WebDAV[RFC2518] protocol for remote web authoring. Thus, there is a
need for a media type to properly label the exchange of XML network
entities. (Note that, as sometimes happens between two communities,
both MIME and XML have defined the term entity, with different
meanings.)

Although XML is a subset of the Standard Generalized Markup Language
(SGML) ISO 8879[SGML], and currently is assigned the media types
text/sgml and application/sgml, there are several reasons why use of
text/sgml or application/sgml to label XML is inappropriate. First,
there exist many applications which can process XML, but which
cannot process SGML, due to SGML's larger feature set. Second, SGML
applications cannot always process XML entities, because XML uses
features of recent technical corrigenda to SGML. Third, the
definition of text/sgml and application/sgml in [RFC1874] includes
parameters for SGML bit combination transformation format
(SGML-bctf), and SGML boot attribute (SGML-boot). Since XML does not
use these parameters, it would be ambiguous if such parameters were
given for an XML MIME entity. For these reasons, the best approach
for labeling XML network entities is to provide new media types for
XML.

Since XML is an integral part of the WebDAV Distributed Authoring
Protocol, and since World Wide Web Consortium Recommendations have
conventionally been assigned IETF tree media types, and since
similar media types (HTML, SGML) have been assigned IETF tree media
types, the XML media types also belong in the IETF media types tree.

Similarly, XML will be used as a foundation for other media types,
including types in every branch of the IETF media types tree. To
facilitate the processing of such types, media types based on XML,
but which are not identified using text/xml or application/xml,
should be named using a suffix of '|xml' as described in Section 8.
This will allow XML-based tools -- browsers, editors, search
engines, and other processors -- to work with all XML-based media
types.

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2. Editor's Notes

In the final version of this document, this section will be removed.
It provides a listing of all the Editor's Notes appearing in this
document. Notes still appear in the document in the section noted.

Section 4.1 - [Editor's note: should we mandate this parameter?
US-ASCII is not a good default, since it is not international.
ISO-8859-1, which is used by HTML 1.1, is not international
either. UTF-8 is international, but is not currently used by MIME
or HTML specifications and implementations. By mandating this
parameter, we do not have to choose one of these unsatisfactory
possibilities and we can very strongly encourage the use of this
parameter. On the other hand, those users who only need US-ASCII
characters will be forced to specify the charset parameter.]

Section 4.1 - [Editor's note: should we say anything about
dispatching based on namespace URIs in this document?]

Section 7 - [Editor's note: one of the authors have sent a
comment to the XML Linking WG and requested not to allow default
values for xml:base.]

Section 8 - [Editor's note: the use of non-XPointer fragment
identifiers by XML vocabularies like SVG and SMIL requires
further discussion.]

Section 10 - [Editor's note: some applications of XML may open up
new security considerations. This issue needs further
consideration.]

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3. 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 [RFC2119].

As defined in [RFC2781], the three charsets "utf-16", "utf-16le",
and "utf-16be" are used to label UTF-16 text. In this document, "the
UTF-16 family" refers to those three charsets. By contrast, the
phrases "utf-16" or UTF-16 in this document refer specifically to
the single charset "utf-16".

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4. XML Media Types

This document introduces five new media types for XML MIME entities,
text/xml, application/xml, text/xml-external-parsed-entity,
application/xml-external-parsed-entity, and application/xml-dtd.
Registration information for these media types is described in the
sections below.

Within the XML specification, XML MIME entities can be classified
into four types. In the XML terminology, they are called "document
entities", "external DTD subsets", "external parsed entities", and
"external parameter entities". The media types text/xml and
application/xml can be used for "document entities", while
text/xml-external-parsed-entity or
application/xml-external-parsed-entity are appropriate for "external
parsed entities". The media type application/xml-dtd can be used for
"external DTD subsets" or "external parameter entities". For
backward compatibility, application/xml and text/xml can also be
used for "external parsed entities", "external DTD subsets", and
"external parameter entities".

Neither external DTD subsets nor external parameter entities parse
as XML documents, and while some XML document entities may be used
as external parsed entities and vice versa, there are many cases
where the two are not interchangeable. XML also has unparsed
entities, internal parsed entities, and internal parameter entities,
but they are not XML MIME entities.

If an XML document -- that is, the unprocessed, source XML document
-- is readable by casual users, text/xml is preferable to
application/xml. MIME user agents (and web user agents) that do not
have explicit support for text/xml will treat it as text/plain, for
example, by displaying the XML entity as plain text. Application/xml
is preferable when the XML MIME entity is unreadable by casual
users. Similarly, text/xml-external-parsed-entity is preferable when
an external parsed entity is readable by casual users, but
application/xml-external-parsed-entity is preferable when a plain
text display is inappropriate.

NOTE: Users are in general not used to text containing tags such
as <price>, and often find such tags quite disorienting or
annoying. If one is not sure, the conservative principle would
suggest using application/* instead of text/* so as not to put
information in front of users that they will quite likely not
understand.

The top-level media type "text" has some restrictions on MIME
entities and they are described in [RFC2045] and [RFC2046]. In
particular, the UTF-16 family, UCS-4, and UTF-32 are not allowed

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(except over HTTP[RFC2616], which uses a MIME-like mechanism). Thus,
if an XML document or external parsed entity is encoded in such
character encoding schemes, it cannot be labeled as text/xml or
text/xml-external-parsed-entity (except for HTTP).

Text/xml and application/xml behave differently when the charset
parameter is not explicitly specified. If the default charset (i.e.,
US-ASCII) for text/xml is inconvenient for some reason (e.g., bad
WWW servers), application/xml provides an alternative (see "Optional
parameters" of application/xml registration in Section 4.2). The
same rules apply to the distinction between
text/xml-external-parsed-entity and
application/xml-external-parsed-entity.

XML provides a general framework for defining sequences of
structured data. In some cases, it may be desirable to define new
media types that use XML but define a specific application of XML,
perhaps due to domain-specific security considerations or runtime
information. Furthermore, such media types may allow UTF-8 or UTF-16
only and prohibit other charsets. This document does not prohibit
such media types and in fact expects them to proliferate. However,
developers of such media types are STRONGLY RECOMMENDED to use this
document as a basis for their registration. In particular, the
charset parameter SHOULD be used in the same manner in order to
enhance interoperability.

4.1 Text/xml Registration

MIME media type name: text

MIME subtype name: xml

Mandatory parameters: none

Optional parameters: charset

[Editor's note: should we mandate this parameter? US-ASCII is not
a good default, since it is not international. ISO-8859-1, which
is used by HTML 1.1, is not international either. UTF-8 is
international and is the IESG recommended charset for new
protocols, but it is not currently used by MIME or HTML
specifications and implementations. By mandating this parameter,
we do not have to choose one of these unsatisfactory
possibilities and we can very strongly encourage the use of this
parameter. On the other hand, those users who only need US-ASCII
characters would be forced to specify the charset parameter.]

Although listed as an optional parameter, the use of the charset
parameter is STRONGLY RECOMMENDED, since this information can be

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used by XML processors to determine authoritatively the character
encoding of the XML MIME entity. The charset parameter can also
be used to provide protocol-specific operations, such as
charset-based content negotiation in HTTP. "utf-8" (see
[RFC2279]) is the recommended value, representing the UTF-8
charset. UTF-8 is supported by all conforming processors of [XML].

If the XML MIME entity is transmitted via HTTP, which uses a
MIME-like mechanism that is exempt from the restrictions on the
text top-level type (see section 19.4.1 of [RFC2616]), "utf-16"
([RFC2781]) is also recommended. UTF-16 is supported by all
conforming processors of [XML]. Since the handling of CR, LF and
NUL for text types in most MIME applications would cause
undesired transformations of individual octets in UTF-16
multi-octet characters, gateways from HTTP to these MIME
applications MUST transform the XML MIME entity from text/xml;
charset="utf-16" to application/xml; charset="utf-16".

Conformant with [RFC2046], if a text/xml entity is received with
the charset parameter omitted, MIME processors and XML processors
MUST use the default charset value of "us-ascii". In cases where
the XML MIME entity is transmitted via HTTP, the default charset
value is still "us-ascii". (Note: There is an inconsistency
between this specification and HTTP/1.1, which uses ISO-8859-1 as
the default for a historical reason. Since XML is a new format, a
new default should be chosen for better I18N. US-ASCII was
chosen, since it is the intersection of UTF-8 and ISO-8859-1 and
since it is already used by MIME.)

There are several reasons why use of
text/sgml or application/sgml to label XML that the charset parameter is inappropriate.
authoritative. First,
there exist many applications which can process XML, but which
cannot process SGML, due some MIME processing engines do transcoding
of MIME bodies of the top-level media type "text" without
reference to SGML's larger feature set. Second, SGML
applications cannot always process XML entities, because XML uses
features any of recent technical corrigenda the internal content. Thus, it is possible
that some agent might change a text/xml;charset="iso-2022-jp" to SGML. Third,
text/xml;charset="utf-8" without modifying the
definition encoding
declaration of text/sgml and application/sgml in RFC 1874[4] includes
parameters for SGML bit combination transformation format (SGML-
bctf), and SGML boot attribute (SGML-boot). Since XML does not use
these parameters, it would be ambiguous if such parameters were
given for an XML document. Second, text/xml must be
compatible with text/plain, since MIME entity. For these reasons, agents that do not
understand text/xml will fallback to handling it as text/plain.
If the best approach charset parameter for labeling XML network entities text/xml were not authoritative,
such fallback would cause data corruption. Third, recent WWW
servers have been improved so that users can specify the charset
parameter. Fourth, [RFC2130] specifies that the recommended
specification scheme is to provide new media types for
XML. the "charset" parameter.

Since XML the charset parameter is authoritative, the charset is not
always declared within an integral part of XML encoding declaration. Thus, special
care is needed when the WebDAV Distributed Authoring
Protocol, and since World Wide Web Consortium Recommendations have
conventionally been assigned IETF tree media types, and since
similar media types (HTML, SGML) have been assigned IETF tree media
types, recipient strips the XML media types also belong in MIME header and
provides persistent storage of the IETF media types tree.

Similarly, received XML will be used as a foundation for other media types,
including types MIME entity
(e.g., in every branch of the IETF media types tree. To
facilitate a file system). Unless the processing of such types, media types based on XML,
but which are not identified using text/xml charset is UTF-8 or application/xml,
should be named using a suffix of -xml. This will allow XML-based
tools - browsers, editors, search engines, and other processors - to
work with all XML-based media types.

, UTF-16,

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1.1 Editor's Notes April 2000

the recipient SHOULD also persistently store information about
the charset, perhaps by embedding a correct XML encoding
declaration within the XML MIME entity.

Encoding considerations: This section will media type MAY be removed by encoded as
appropriate for the final draft of this document.
It provides a listing charset and the capabilities of all the Editor's Notes appearing
underlying MIME transport. For 7-bit transports, data in this
document. Notes still appear either
UTF-8 or UTF-16 MUST be encoded in the document quoted-printable or base64.
For 8-bit clean transport (e.g., 8BITMIME[RFC1652] ESMTP or
NNTP[RFC0977]), UTF-8 is not encoded, but UTF-16 MUST be encoded
in the section noted.

General - [Editor's note: should we replace
'external-parsed-entity' with 'epse'?]

3.1 - base64.For binary clean transports (e.g., HTTP[RFC2616]), no
content-transfer-encoding is necessary.

Security considerations: See Section 10.

Interoperability considerations: XML has proven to be interoperable
across WebDAV clients and servers, and for import and export from
multiple XML authoring tools.

Published specification: Extensible Markup Language (XML) 1.0[XML]

Applications which use this media type: XML is device-, platform-,
and vendor-neutral and is supported by a wide range of Web user
agents, WebDAV[RFC2518] clients and servers, as well as XML
authoring tools. [Editor's note: should we say anything about
dispatching based on namespace URIs in this document?]

3.2 - [Editor's note: should we say anything about dispatching
based

Additional information:

Magic number(s): None.

Although no byte sequences can be counted on namespace URIs to always be
present, XML MIME entities in this document?]

4. - [Editor's note: some applications ASCII-compatible charsets
(including UTF-8) often begin with hexadecimal 3C 3F 78 6D 6C
("<?xml"), and those in UTF-16 often begin with hexadecimal FE
FF 00 3C 00 3F 00 78 00 6D or FF FE 3C 00 3F 00 78 00 6D 00
(the Byte Order Mark (BOM) followed by "<?xml"). For more
information, see Annex F of XML may open up new
security considerations. This issue needs [XML].

File extension(s): .xml

Macintosh File Type Code(s): "TEXT"

Person and email address for further consideration.]

6. - [Editor's note: information:

Murata Makoto (Family Given) <mura034@attglobal.net>

Simon St.Laurent <simonstl@simonstl.com>

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Daniel Kohn <dan@dankohn.com>

Intended usage: COMMON

Author/Change controller: The XML specification is a work product of
the World Wide Web Consortium's XML Working Group, and was edited
by:

Tim Bray <tbray@textuality.com>

Jean Paoli <jeanpa@microsoft.com>

C. M. Sperberg-McQueen <cmsmcq@uic.edu>

The W3C, and the W3C XML Core Working Group, have change control
over the XML specification.

4.2 Application/xml Registration

MIME media type name: application

MIME subtype name: xml

Mandatory parameters: none

Optional parameters: charset

Although listed as an optional parameter, the use of non-XPointer fragment identifiers the charset
parameter is STRONGLY RECOMMENDED, since this information can be
used by XML vocabularies like SVG and SMIL requires further
discussion.]

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of the XML Media Types December 1999

2. Notational Conventions MIME entity. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", charset parameter can also be used to
provide protocol-specific operations, such as charset-based
content negotiation in HTTP.

"utf-8" (see [RFC2279]) and "OPTIONAL" "utf-16" ([RFC2781]) are the
recommended values, representing the UTF-8 and UTF-16 charsets,
respectively. These charsets are preferred since they are
supported by all conforming processors of [XML].

If an application/xml entity is received where the charset
parameter is omitted, no information is being provided about the
charset by the MIME Content-Type header. Conforming XML
processors MUST follow the requirements in section 4.3.3 of [XML]
that directly address this
document contingency. However, MIME processors
that are to be interpreted as described in RFC 2119[8].

, not XML processors should not assume a default charset
if the charset parameter is omitted from an application/xml
entity.

Since the charset parameter is authoritative, the charset is not

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3. XML Media Types

This document introduces five new media types for April 2000

always declared within an XML encoding declaration. Thus, special
care is needed when the recipient strips the MIME entities,
text/xml, application/xml, text/xml-external-parsed-entity,
application/xml-external-parsed-entity, header and application/xml-dtd.
Registration information for these media types are described
provides persistent storage of the received XML MIME entity
(e.g., in a file system). Unless the
sections below.

Within charset is UTF-8 or UTF-16,
the recipient SHOULD also persistently store information about
the charset, perhaps by embedding a correct XML specification, XML MIME entities can be classified
into four types. In encoding
declaration within the XML terminology, they are called "document
entities", "external DTD subsets", "external parsed entities", and
"external parameter entities". The media types text/xml and
application/xml can be used MIME entity.

Encoding considerations Same as those for "document entities", while "external
parsed entities" require text/xml-external-parsed-entity or
application/xml-external-parsed-entity. For backward compatibility,
application/xml and text/xml can also be used for "external parsed
entities", "external DTD subsets", as described in
Section 4.1.

Security considerations: See Section 10.

Interoperability considerations: Same as Section 4.1.

Published specification: Same as Section 4.1.

Applications which use this media type: Same as Section 4.1.

Additional information: Same as Section 4.1.

Person and "external parameter
entities". The email address for further information: Same as Section
4.1.

Intended usage: COMMON

Author/Change controller: Same as Section 4.1.

4.3 Text/xml-external-parsed-entity Registration

MIME media type application/xml-dtd can be used for
"external DTD subsets" or "external name: text

MIME subtype name: xml-external-parsed-entity

Mandatory parameters: none

Optional parameters: charset

The charset parameter entities". Neither
external DTD subsets nor of text/xml-external-parsed-entity is
handled the same as that of text/xml as described in Section 4.1.

Encoding considerations: Same as Section 4.1.

Security considerations: See Section 10.

Interoperability considerations: XML external parameter parsed entities parse are as
interoperable as XML documents, though they have a less tightly
constrained structure and while some therefore need to be referenced by XML document entities may
documents for proper handling by XML processors. Similarly, XML

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documents cannot be reliably used as external parsed entities and vice versa, there are many cases where
the two
because external parsed entities are not interchangeable. prohibited from having
standalone document declarations or DTDs. Identifying XML also has unparsed entities,
internal
external parsed entities, entities with their own content type should
enhance interoperability of both XML documents and internal parameter entities, but they
are not XML MIME external
parsed entities.

If an

When non-validating processors handle XML document is readable by casual users, text/xml is
preferable to application/xml. MIME user agents (and web user
agents) that documents, they do not have explicit support for text/xml will treat it
always read external parsed entities. Thus, interoperability is
not guaranteed.

Published specification: Same as text/plain, Section 4.1.

Applications which use this media type: Same as Section 4.1.

Additional information:

Magic number(s): Same as Section 4.1.

File extension(s): .xml or .ent

Macintosh File Type Code(s): "TEXT"

Person and email address for example, by displaying the XML entity further information: Same as plain
text. Application/xml Section
4.1.

Intended usage: COMMON

Author/Change controller: Same as Section 4.1.

4.4 Application/xml-external-parsed-entity Registration

MIME media type name: application

MIME subtype name: xml-external-parsed-entity

Mandatory parameters: none

Optional parameters: charset

The charset parameter of application/xml-external-parsed-entity
is preferable when handled the same as that of application/xml as described in
Section 4.2.

Encoding considerations: Same as Section 4.2.

Security considerations: See Section 10.

Interoperability considerations: Same as those for

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Internet-Draft XML MIME entity is
unreadable by casual users. Similarly, Media Types April 2000

text/xml-external-parsed-entity is preferable when an external
parsed entity is readable by casual users, but
application/xml-external-parsed-entity is preferable when a plain
text display is inappropriate.

The top-level as described in Section 4.3.

Published specification: Same as text/xml as described in Section
4.1.

Applications which use this media type: Same as Section 4.1.

Additional information:

Magic number(s): Same as Section 4.1.

File extension(s): .xml or .ent

Macintosh File Type Code(s): "TEXT"

Person and email address for further information: Same as Section
4.1.

Intended usage: COMMON

Author/Change controller: Same as Section 4.1.

4.5 Application/xml-dtd Registration

MIME media type "text" has some restrictions on name: application

MIME
entities and they are subtype name: xml-dtd

Mandatory parameters: none

Optional parameters: charset

The charset parameter of application/xml-dtd is handled the same
as that of application/xml as described in RFC 2045[5] and RFC 2046[6]. In
particular, UTF-16, UCS-4, Section 4.2.

Encoding considerations: Same as Section 4.2.

Security considerations: See Section 10.

Interoperability considerations: XML DTDs have proven to be
interoperable by DTD authoring tools and UTF-32 are not allowed (except for
HTTP, which uses a MIME-like mechanism). Thus, if an XML document
or browsers, among
others.

Note, however, that some XML processors do not read external parsed entity is encoded in such character encoding
schemes, it cannot be labled as text/xml DTD
subsets or
text/xml-external-parsed-entity (except for HTTP).

Text/xml and application/xml behave differently when the charset external parameter entities. Thus, interoperability is
not explicitly specified. If the default charset
(i.e., US-ASCII) for guaranteed.

Published specification: Same as text/xml is inconvenient for some reason (e.g.,
bad WWW servers), application/xml provides an alternative (see

, as described in Section
4.1.

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"Optional parameters" of "3.2 Application/xml Registration"). The
same rules apply to the distinction between
text/xml-external-parsed-entity and
application/xml-external-parsed-entity.

XML provides a general framework for defining sequences of
structured data. In some cases, it may be desirable to define new
media types April 2000

Applications which use this media type: DTD authoring tools handle
external DTD subsets as well as external parameter entities. XML but define a specific application of XML,
perhaps due to domain-specific security considerations
browsers may also access external DTD subsets and external
parameter entities.

Additional information:

Magic number(s): Same as Section 4.1.

File extension(s): .dtd or runtime
information. This document does not prohibit future media types
dedicated .mod

Macintosh File Type Code(s): "TEXT"

Person and email address for further information: Same as Section
4.1.

Intended usage: COMMON

Author/Change controller: Same as Section 4.1.

4.6 Summary

The following list applies to such XML applications. However, developers of such text/xml,
text/xml-external-parsed-entity, and XML-based media types are recommended to use this document as a basis. In
particular, the charset parameter should be used in under the same manner.

3.1 Text/xml Registration

MIME media
top-level type name: text

MIME subtype name: xml

Mandatory parameters: none

Optional parameters: charset

Although listed as an optional parameter, the use of "text" that define the charset parameter is STRONGLY RECOMMENDED, since this information can be
used by XML processors according to determine authoritatively the character
encoding of the XML MIME entity. The charset
this specification:

o Charset parameter can also be
used to provide protocol-specific operations, such as charset-based
content negotiation in HTTP. "UTF-8" (see RFC 2279[9]) is the strongly recommended value, representing the UTF-8 charset. UTF-8 is
supported by all conforming processors of XML 1.0[10].

o If the XML MIME entity is transmitted via HTTP, which uses a
MIME-like mechanism that charset parameter is exempt from the restrictions on not specified, the text
top- level type (see section 19.4.1 of RFC 2616[13])), "UTF-16"
(Appendix C.3 of Unicode 3.0[14] and Amendment 1 of ISO/IEC
10646[2]) is also recommended. UTF-16 default is supported by all
conforming processors of XML 1.0[10] . Since the handling of CR, LF
and NUL for text types in most MIME applications would cause
undesired transformations
"us-ascii". The default of individual octets "iso-8859-1" in UTF-16 multi-octet
characters, gateways from HTTP is explicitly
overridden.

o No error handling provisions.

o An encoding declaration, if present, is irrelevant, but when
saving a received resource as a file, the correct encoding
declaration should be inserted.

The next list applies to these MIME applications MUST
transform application/xml,
application/xml-external-parsed-entity, application/xml-dtd, and
XML-based media types under top-level types other than "text" that
define the XML MIME entity from a text/xml; charset="utf-16" charset parameter according to
application/xml; charset="utf-16".

Conformant with RFC 2046[6], if a text/xml entity this specification:

o Charset parameter is received with strongly recommended, and if present, it
takes precedence.

o If the charset parameter is omitted, MIME processors and conforming XML processors
MUST use follow the default charset value requirements in section 4.3.3 of "us-ascii". In cases where
the XML MIME entity is transmitted via HTTP, the default charset

, [XML].

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value is still "us-ascii". (Note: There is an inconsistency
between this specification and HTTP/1.1, which uses "ISO-8859-1" as
the default for a historical reason. Since XML is a new format, a
new default should be chosen for better I18N. "US-ASCII" was chosen
as April 2000

4.7 Referencing

New media type registrations under the intersection of "UTF-8" and "ISO-8859-1".)

One reason that top-level type "text" SHOULD,
in specifying the charset parameter, define it as: "Same as charset
parameter is authoritative is that some
MIME processing engines do transcoding of MIME bodies of the
top-level text/xml as specified in RFC XXXX."

New media type registrations under top-level types other than "text" without reference to any of
SHOULD, in specifying the internal
content. Thus, charset parameter, define it is possible that some agent might change a
text/xml;charset=iso-2022-jp to text/xml;charset=UTF-8 without
modifying as: "Same as
charset parameter of application/xml as specified in RFC XXXX."

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5. The Byte Order Mark (BOM) and Conversions to/from the encoding declaration UTF-16 Charset

Section 4.3.3 of an [XML] specifies that XML document.

Since MIME entities in the
charset parameter "utf-16" must begin with a byte order mark (BOM), which is authoritative, a
hexadecimal octet sequence 0xFE 0xFF (or 0xFF 0xFE, depending on
endian). The XML Recommendation further states that the charset BOM is not
always declared within an XML
encoding declaration. Thus, special
care signature, and is needed when not part of either the recipient strips markup or the MIME header and
provides persistent storage
character data of the received XML MIME entity (e.g.,
in a file system). Unless the charset is UTF-8 or UTF-16, document.

Due to the
recipient SHOULD also persistently store information about presence of the
charset, perhaps by embedding a correct BOM, applications which convert XML from
"utf-16" to a non-Unicode encoding declaration
within MUST strip the XML MIME entity.

Encoding considerations:

This media type MAY BOM before
conversion. Similarly, when converting from another encoding into
"utf-16", the BOM MUST be encoded as appropriate for added after conversion is complete.

In addition to the charset and
the capabilities of the underlying "utf-16", [RFC2781] introduces "utf-16le"
(little endian) and "utf-16be" (big endian) as well. The BOM is
prohibited for these charsets. When an XML MIME transport. For 7-bit
transports, data in both UTF-8 and UTF-16 entity is encoded in quoted-
printable or base64. For 8-bit clean transport (e.g., 8BITMIME
ESMTP
"utf-16le" or NNTP), UTF-8 is "utf-16be", it MUST not encoded, begin with the BOM but UTF-16 is base64 encoded.
For binary clean transports (e.g., HTTP), no content-
transfer-encoding is necessary.

Security considerations:

See section 4 below.

Interoperability considerations:

XML has proven SHOULD
contain an encoding declaration. Conversion from "utf-16" to be interoperable across WebDAV clients and
servers, and for import
"utf-16be" or "utf-16le" and export from multiple XML authoring tools.

Published specification:

see XML 1.0[10]

Applications which use this media type: conversion in the other direction MUST
strip or add the BOM, respectively.

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6. Fragment Identifiers

[RFC2396] notes that the semantics of a fragment identifier (the
part of a URI after a "#") is device-, platform-, a property of the data resulting from
a retrieval action, and vendor-neutral that the format and interpretation of
fragment identifiers is supported dependent on the media type of the retrieval
result.

For documents labeled as text/xml or application/xml, the fragment
identifier is an escaped XPointer represented in US-ASCII. An
XPointer in UTF-8 is constructed from this escaped XPointer by
converting %HH to a
wide range byte of Web user agents, WebDAV clients and servers, as well

, the hexadecimal value HH. XPointers are
described in detail in [XPtr]; in particular, escaping (i.e., the
use of %HH for non-allowed characters) is described in section 2.2.

If an XML-based media type requires a fragment identifier format
other than escaped XPointers, the media type SHOULD NOT follow the
naming convention for XML-based media types (a suffix of '|xml').

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as XML authoring tools.

[Editor's note: should we say anything about dispatching based on
namespace URIs April 2000

7. The Base URI

Section 5.1 of RFC 2396[RFC2396] specifies that the semantics of a
relative URI reference embedded in this document?]

Additional information:

Magic number(s): none

Although no byte sequences can be counted on to always be present,
XML a MIME entities entity is dependent on the
base URI. The base URI is either (1) the base URI embedded in ASCII-compatible charsets (including UTF-8)
often begin with hexadecimal 3C 3F 78 6D 6C ("<?xml"). For more
information, see Appendix F the
MIME entity, (2) the base URI of XML 1.0[10].

File extension(s): .xml

Macintosh File Type Code(s): "TEXT"

Person & email address for the encapsulating MIME entity, (3)
the URI used to retrieve the MIME entity, or (4) the
application-dependent default base URI, where (1) has the highest
precedence.[RFC2396] further information:

Murata Makoto (Family Given) <mura034@attglobal.net>

Simon St.Laurent <simonstl@simonstl.com>

Intended usage: COMMON

Author/Change controller: specifies that the mechanism for
embedding the base URI is dependent on the media type.

The XML specification media type dependent mechanism for embedding the base URI in a
MIME entity of type text/xml, application/xml,
text/xml-external-parsed-entity, or
application/xml-external-parsed-entity is to use the xml:base
attribute described in detail in [XBase].

Note that the base URI may be embedded in a work product of different MIME entity,
since the World Wide Web
Consortium's XML Working Group, and was edited by:

Tim Bray <tbray@textuality.com>

Jean Paoli <jeanpa@microsoft.com>

C. M. Sperberg-McQueen <cmsmcq@uic.edu>

The W3C, and default value for the W3C XML Core Working Group, xml:base attribute may be specified
in an external DTD subset or external parameter entity, which is
labeled as application/xml-dtd.[Editor's note: one of the authors
have change control
over sent a comment to the XML specification.

3.2 Application/xml Registration

MIME media type name: application

MIME subtype name: xml

Mandatory parameters: none

Optional parameters: charset

, Linking WG and requested not to allow
default values for xml:base.]

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Although listed as an optional parameter, April 2000

8. A Naming Convention for XML-Based Media Types

This document recommends the use of the charset
parameter is STRONGLY RECOMMENDED, since this information can be
used by XML processors to determine authoritatively the charset a naming convention (a suffix of
the XML
'|xml') for identifying XML-based MIME entity. The charset parameter can also be used to
provide protocol-specific operations, such as charset-based media types, whatever their
particular content
negotiation in HTTP.

"UTF-8" (see RFC 2279[9]) and "UTF-16" (Appendix C.3 may represent. This allows the use of Unicode
3.0[14] generic XML
processors and Amendment 1 technologies on a wide variety of ISO/IEC 10646[2]) are the recommended
values, representing different XML
document types at a minimum cost, using existing frameworks for
media type registration.

Although the UTF-8 and UTF-16 charsets, respectively.
These charsets are preferred since they are supported by all
conforming processors use of a suffix was not considered as part of XML 1.0[10].

If an application/xml entity is received where the charset parameter
is omitted, no information
original MIME architecture, this choice is being provided about considered to provide the charset by
most functionality with the MIME Content-Type header. Conforming XML processors MUST follow least potential for interoperability
problems or lack of future extensibility. The alternatives to the requirements
'|xml' suffix and the reason for its selection are described in section 4.3.3 of
Appendix A.

As XML 1.0[10] which directly
address this contingency. However, MIME processors which development continues, new XML document types are not appearing
rapidly. Many of these XML
processors should not assume a default charset if the charset
parameter is omitted document types would benefit from an application/xml entity.

Since the charset parameter is authoritative, the charset is not
always declared within an XML encoding declaration. Thus, special
care
identification possibilities of a more specific MIME media type than
text/xml or application/xml can provide, and it is needed when likely that many
new media types for XML-based document types will be registered in
the recipient strips near and ongoing future.

While the benefits of specific MIME header and
provides persistent storage types for particular types of the received
XML MIME entity (e.g.,
in a file system). Unless the charset documents are significant, all XML documents share common
structures and syntax that make possible common processing.

Some areas where 'generic' processing is UTF-8 useful include:

o Browsing - An XML browser can display any XML document with a
provided [CSS] or UTF-16, [XSLT] style sheet, whatever the
recipient SHOULD also persistently store information about vocabulary of
that document.

o Editing - Any XML editor can read, modify, and save any XML
document.

o Fragment identification - XPointers[XPtr] can work with any XML
document, whatever vocabulary it uses and whether or not it uses
XPointer for its own fragment identification. [Editor's note: the
charset, perhaps
use of non-XPointer fragment identifiers by embedding a correct XML encoding declaration
within the vocabularies like
SVG and SMIL requires further discussion.]

o Hypertext Linking - [XLink] hypertext linking is designed to
connect any XML MIME entity.

Encoding considerations:

This media type MAY documents, regardless of vocabulary.

o Searching - XML-oriented search engines, web crawlers, agents,
and query tools should be encoded as appropriate for able to read XML documents and extract
the charset names and content of elements and attributes even if the capabilities
tools are ignorant of the underlying MIME transport. For 7-bit
transports, data in both UTF-8 and UTF-16 is encoded in quoted-
printable or base64. For 8-bit clean transport (e.g., 8BITMIME
ESMTP or NNTP), UTF-8 is not encoded, but UTF-16 is base64 encoded.
For binary clean transport (e.g., HTTP), no content-
transfer-encoding is necessary.

Security considerations:

See section 4 below.

Interoperability considerations:

XML has proven to be interoperable particular vocabulary used for import and export from
multiple XML authoring tools.

, elements

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Published specification:

see April 2000

and attributes.

o Storage - XML-oriented storage systems, which keep XML documents
internally in a parsed form, should similarly be able to process,
store, and recreate any XML document.

o Well-formedness and validity checking - An XML processor can
confirm that any XML document is well-formed and that it is valid
(i.e., conforms to its declared DTD or Schema).

When a new media type is introduced for an XML-based format, the
name of the media type SHOULD end with '|xml'. This convention will
allow applications that can process XML generically to detect that
the MIME entity is supposed to be an XML 1.0[10]

Applications which use document, verify this media type:
assumption by invoking some XML is device-, platform-, and vendor-neutral processor, and is supported then process the XML
document accordingly. Applications may match for types that
represent XML entities by a
wide range comparing the subtype to the pattern
'*/*|xml'. (Of course, 4 of Web user agents and XML authoring tools.

[Editor's note: should we say anything about dispatching based on
namespace URIs the 5 media types defined in this document?]

Additional information:

Magic number(s): none

Although no byte sequences can be counted on to always be present,
document -- text/xml, application/xml,
text/xml-external-parsed-entity, and
application/xml-external-parsed-entity -- also represent XML MIME
entities in ASCII-compatible charsets (including UTF-8)
often begin with hexadecimal 3C 3F 78 6D 6C ("<?xml"), while not conforming to the '*/*|xml' pattern.)

NOTE: Section 14.1 of HTTP[RFC2616] does not support Accept
headers of the form "Accept: */*|xml" and those so this header MUST NOT
be used in
UTF-16 often begin with hexadecimal FE FF 00 3C 00 3F 00 78 00 6D or
FF FE 3C 00 3F 00 78 00 6D 00 (the Byte Order Mark (BOM) followed by
"<?xml"). For more information, see Annex F of this way. Instead, content negotiation[RFC2703] could
potentially be used if an XML-based MIME type is needed.

XML 1.0[10].

File extension(s): .xml

Macintosh File Type Code(s): "TEXT"

Person & email address generic processing is not always appropriate for further information:

See XML-based media
types. For example, authors of some such media types may wish that
the types remain entirely opaque except to applications that are
specifically designed to deal with that media type. By NOT following
the naming convention '|xml', such media types can avoid XML-generic
processing. Since generic processing will be useful in many cases,
however -- including in some situations that are difficult to
predict ahead of time -- those registering media types SHOULD use
the '|xml' convention unless they have a particularly compelling
reason not to.

The registration of text/xml.

Intended usage: COMMON

Author/Change controller: process for these media types is described in
[RFC2048]. The same as registrar for the author/change controller of text/xml.

3.3 text/xml-external-parsed-entity Registration

MIME IETF tree will encourage new
XML-based media type name: text

MIME subtype name: xml-external-parsed-entity

Mandatory parameters: none

Optional parameters: charset registrations in the IETF tree to follow this
guideline. Registrars for other trees SHOULD follow this convention
in order to ensure maximum interoperability of their XML-based
documents. Similarly, media subtypes that do not represent XML
entities MUST NOT be allowed to register with a '|xml' suffix.

The optional charset parameter SHOULD be used with XML-based media
types and its use SHOULD be specified as described in Section 4.7.

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The use of text/xml-external-parsed-entity the charset parameter is handled
exactly STRONGLY RECOMMENDED, since this
information can be used by XML processors to determine
authoritatively the same as that charset of text/xml.

, the XML MIME entity.

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Encoding considerations: April 2000

9. Examples

The encoding considerations examples below give the value of text/xml apply.

Security considerations:

See section 4 below.

Interoperability considerations: the MIME Content-type header
and the XML external parsed entities are as interoperable as declaration (which includes the encoding declaration)
inside the XML documents,
though they have a less tightly constrained structure MIME entity. For UTF-16 examples, the Byte Order Mark
character is denoted as "{BOM}", and must
therefore be referenced by XML documents for proper handling by the XML
processors. Similarly, declaration is assumed
to come at the beginning of the XML documents cannot MIME entity, immediately
following the BOM. Note that other MIME headers may be reliably used as
external parsed entities because external parsed entities are
prohibited from using present, and
the standalone declaration XML MIME entity may contain other data in addition to the XML
declaration. Identifying XML external parsed entities
declaration; the examples focus on the Content-type header and the
encoding declaration for clarity.

9.1 Text/xml with their own
content type should enhance interoperability of both XML documents UTF-8 Charset

Content-type: text/xml; charset="utf-8"

<?xml version="1.0" encoding="utf-8"?>

This is the recommended charset value for use with text/xml. Since
the charset parameter is provided, MIME and XML external parsed entities.

Since non-validating processors of XML 1.0 do not always read
external parsed entities, interoperability is not guaranteed.

Published specification:

see must
treat the enclosed entity as UTF-8 encoded.

If sent using a 7-bit transport (e.g. SMTP[RFC0821]), the XML 1.0[10]

Applications which entity
must use this media type:

Applications a content-transfer-encoding of text/xml either quoted-printable or application/xml may use external parsed
entities.

[Editor's note: should we say anything about dispatching based on
namespace URIs in this document?]

Additional information:

Magic number(s): none

The same as magic numbers for text/xml.

File extension(s): .xml

Macintosh File Type Code(s): "TEXT"

Person & email address for further information:

See
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.

9.2 Text/xml with UTF-16 Charset

Content-type: text/xml; charset="utf-16"

{BOM}<?xml version='1.0' encoding='utf-16'?>

{BOM}<?xml version='1.0'?>

This is possible only when the XML MIME entity is transmitted via
HTTP, which uses a MIME-like mechanism and is a binary-clean
protocol, hence does not perform CR and LF transformations and
allows NUL octets. As described in [RFC2781], utf-16 charset may not
be used with media types under the registration top-level type "text" except over
HTTP (see section 19.4.1 of text/xml.

, [RFC2616] for details).

Since HTTP is binary clean, no content-transfer-encoding is
necessary.

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Intended usage: COMMON

Author/Change controller:

The same as April 2000

9.3 Text/xml with UTF-16BE Charset

Content-type: text/xml; charset="utf-16be"

<?xml version='1.0' encoding='utf-16be'?>

Observe that the author/change controller of text/xml.

3.4 application/xml-external-parsed-entity Registration

MIME media type name: application BOM does not exist. This is again possible only
when the XML MIME subtype name: xml-external-parsed-entity

Mandatory parameters: none

Optional parameters: entity is transmitted via HTTP.

9.4 Text/xml with ISO-2022-KR Charset

Content-type: text/xml; charset="iso-2022-kr"

<?xml version="1.0" encoding='iso-2022-kr'?>

This example shows text/xml with a Korean charset

The (e.g., Hangul)
encoded following the specification in [RFC1557]. Since the charset
parameter of application/xml-external-parsed-entity is
handled exactly provided, MIME and XML processors must treat the same
enclosed entity as that of application/xml.

Encoding considerations:

The encoding considerations of application/xml apply.

Security considerations:

See section 4 below.

Interoperability considerations:

The interoperability considerations of
text/xml-external-parsed-entity apply.

Published specification:

see XML 1.0[10]

Applications which encoded per RFC 1557.

Since ISO-2022-KR has been defined to use this media type:

Applications only 7 bits of data, no
content-transfer-encoding is necessary with any transport.

9.5 Text/xml with Omitted Charset

Content-type: text/xml

{BOM}<?xml version="1.0" encoding="utf-16"?>

or application/xml may use external parsed
entities.

[Editor's note: should we say anything about dispatching based on
namespace URIs in

{BOM}<?xml version="1.0"?>

This example shows text/xml with the charset parameter omitted. In
this document?]

Additional information:

Magic number(s): none case, MIME and XML processors must assume the charset is
"us-ascii", the default charset value for text media types specified
in [RFC2046]. The same as magic numbers default of "us-ascii" holds even if the text/xml
entity is transported using HTTP.

Omitting the charset parameter is NOT RECOMMENDED for text/xml.

, For
example, even if the contents of the XML MIME entity are UTF-16 or
UTF-8, or the XML MIME entity has an explicit encoding declaration,
XML and MIME processors must assume the charset is "us-ascii".

9.6 Application/xml with UTF-16 Charset

Content-type: application/xml; charset="utf-16"

{BOM}<?xml version="1.0" encoding="utf-16"?>

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File extension(s): .xml

Macintosh File Type Code(s): "TEXT"

Person & email address April 2000

{BOM}<?xml version="1.0"?>

This is a recommended charset value for further information:

See the registration of text/xml.

Intended usage: COMMON

Author/Change controller:

The same as use with application/xml.
Since the author/change controller of text/xml.

3.5 Application/xml-dtd Registration

MIME media type name: application

MIME subtype name: xml-dtd

Mandatory parameters: none

Optional parameters: charset

The charset parameter of application/xml-dtd is handled exactly provided, MIME and XML processors
must treat the
same enclosed entity as that of application/xml.

Encoding considerations:

The encoding considerations of application/xml apply.

Security considerations:

See section 4 below.

Interoperability considerations: 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 DTDs has proven to MIME entity must
be interoperable by DTD authoring tools and
XML WWW browsers among others.

Published specification: see XML 1.0[10]

Applications which use this media type:

DTD authoring tools handle external DTD subsets as well as external encoded in quoted-printable or base64. For a binary clean
transport (e.g., HTTP), no content-transfer-encoding is necessary.

9.7 Application/xml with UTF-16BE Charset

Content-type: application/xml; charset="utf-16be"

<?xml version='1.0' encoding='utf-16be'?>

Observe that the BOM does not exist. Since the charset parameter entities. XML browsers may also access external DTD
subests is
provided, MIME and external parameter entities.

Additional information:

, et. al. Expires May 31, 2000 [Page 14]

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Magic number(s): none

The same as magic numbers for application/xml.

File extension(s): .dtd

Macintosh File Type Code(s): "TEXT"

Person & email address for further information:

See processors must treat the registration of text/xml.

Intended usage: COMMON

Author/Change controller:

The same enclosed entity as
UTF-16BE encoded.

9.8 Application/xml with ISO-2022-KR Charset

Content-type: application/xml; charset="iso-2022-kr"

<?xml version="1.0" encoding="iso-2022-kr"?>

This example shows application/xml with a Korean charset (e.g.,
Hangul) encoded following the author/change controller of text/xml.

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Internet-Draft specification in [RFC1557]. Since the
charset parameter is provided, MIME and XML Media Types December 1999

4. Security Considerations

XML, as a subset of SGML, has processors must treat
the same security considerations enclosed entity as
specified in encoded per RFC 1874[4]. [Editor's note: some applications of XML
may open up new security considerations. This issue needs further
consideration.]

To paraphrase section 3 1557, independent of RFC 1874[4], whether
the XML MIME entities contain
information entity has an internal encoding declaration (this
example does show such a declaration, which agrees with the charset
parameter).

Since ISO-2022-KR has been defined to be parsed use only 7 bits of data, no
content-transfer-encoding is necessary with any transport.

9.9 Application/xml with Omitted Charset and processed by the recipient's UTF-16 XML
system. These entities may contain and such systems may permit
explicit system level commands to be executed while processing MIME Entity

Content-type: application/xml

{BOM}<?xml version='1.0' encoding="utf-16"?>

{BOM}<?xml version='1.0'?>

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For this example, the
data. To XML MIME entity begins with a BOM. Since the extent that an
charset has been omitted, a conforming XML system will execute arbitrary
command strings, recipients processor follows the
requirements of [XML], section 4.3.3. Specifically, the XML MIME entities may be at risk. In
general, it may be possible to specify commands
processor reads the BOM, and thus knows deterministically that perform
unauthorized file operations or the
charset is UTF-16.

An XML-unaware MIME processor should make changes to no assumptions about the display
processor's environment that affect subsequent operations.

Use
charset of the XML is expected to be varied, MIME entity.

9.10 Application/xml with Omitted Charset and widespread. XML is under
scrutiny by a wide range of communities for use as a common syntax
for community-specific metadata. For UTF-8 Entity

Content-type: application/xml

<?xml version='1.0'?>

In this example, the Dublin Core group
is using XML for document metadata, and a new effort charset parameter has begun which been omitted, and there
is considering use of XML for medical information. Other groups
view no BOM. Since there is no BOM, the XML as a processor follows the
requirements in section 4.3.3, and optionally applies the mechanism for marshalling parameters for remote
procedure calls. More uses
described in appendix F (which is non-normative) of XML will undoubtedly arise.

Security considerations will vary by domain [XML] to
determine the charset encoding of use. For example, UTF-8. The XML medical records will have much more stringent privacy and
security considerations than entity does not
contain an encoding declaration, but since the encoding is UTF-8,
this is still a conforming XML library metadata. Similarly, use MIME entity.

An XML-unaware MIME processor should make no assumptions about the
charset of the XML as a MIME entity.

9.11 Application/xml with Omitted Charset and Internal Encoding
Declaration

Content-type: application/xml

<?xml version='1.0' encoding="iso-10646-ucs-4"?>

In this example, the charset parameter marshalling syntax necessitates a case by case
security review. has been omitted, and there
is no BOM. However, the XML may also MIME entity does have some of an encoding
declaration inside the same security concerns as plain text.
Like plain text, XML can contain escape sequences which, when
displayed, have MIME entity which specifies the potential to change entity's
charset. Following the display processor
environment requirements in ways that adversely affect subsequent operations.
Possible effects include, but are not limited to, locking section 4.3.3, and optionally
applying 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 mechanism described in appendix F (non-normative) of
[XML], the display XML processor a character sequence. If
this is possible determines the display charset encoding 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

, 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.

9.12 Text/xml-external-parsed-entity with UTF-8 Charset

Content-type: text/xml-external-parsed-entity; charset="utf-8"

<?xml encoding="utf-8"?>

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remotely, making it possible for a text display operation to
directly perform some unwanted action. As such, April 2000

This is the ability to
program keys should be blocked either by filtering or by disabling recommended charset value for use with
text/xml-external-parsed-entity. Since the ability to program keys entirely.

Note that it charset parameter is also possible to construct XML documents which make
use of what
provided, MIME and XML terms "entity references" (using processors must treat the enclosed entity as
UTF-8 encoded.

If sent using a 7-bit transport (e.g. SMTP), the XML meaning 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.

9.13 Application/xml-external-parsed-entity with UTF-16 Charset

Content-type: application/xml-external-parsed-entity;
charset="utf-16"

{BOM}<?xml encoding="utf-16"?>

{BOM}<?xml?>

This is a recommended charset value for use with
application/xml-external-parsed-entity. Since the term "entity", which differs from the charset parameter
is provided, MIME definition of this
term), to construct repeated expansions of text. Recursive
expansions are prohibited by XML 1.0[10] and XML processors are
required to detect them. However, even non-recursive expansions may
cause problems 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.

9.14 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 finite computing resources of computers, if
they are performed many times.

, enclosed entity as UTF-16BE encoded.

9.15 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

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5. The Byte Order Mark (BOM) April 2000

application/xml-dtd. Since the charset parameter is provided, MIME
and Conversions to/from UTF-16

The XML Recommendation, in section 4.3.3, specifies that UTF-16 XML
MIME entities processors must begin with a byte order mark (BOM), which is treat the
ZERO WIDTH NO-BREAK SPACE character, hexadecimal sequence 0xFEFF (or
0xFFFE, depending on endian). The enclosed entity as UTF-8 encoded.

9.16 Application/mathml|xml

Content-type: application/mathml|xml

<?xml version="1.0" ?>

MathML documents are XML Recommendation further states
that the BOM is an encoding signature, and is not part of either the
markup or the character data of 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.

9.17 Application/xslt|xml

Content-type: application/xslt|xml

<?xml version="1.0" ?>

Extensible Stylesheet Language (XSLT) documents are XML document.

Due to the BOM, applications which convert documents
whose content describes stylesheets for other XML from documents, as
defined by [XSLT]. As a format based on XML, XSLT documents should
use the UTF-16
encoding to another encoding SHOULD strip '|xml' suffix convention in their MIME content-type
identifier.

9.18 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 BOM before conversion.
Similarly, when converting from another encoding into UTF-16, '|xml' suffix convention
in their MIME content-type identifier.

9.19 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
BOM SHOULD be added after conversion is complete.

, '|xml' suffix
convention in their MIME content-type identifier.

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6. A naming convention for XML-based media types

This document proposes the use of April 2000

10. Security Considerations

XML, as a naming convention (a suffix subset of
'-xml') for identifying XML-based MIME media types, whatever their
particular contents may represent. This allows the use SGML, has all of generic
XML processors the same security
considerations as specified in [RFC1874], and technologies on a wide variety likely more, due to
its expected ubiquitous deployment.

To paraphrase section 3 of different RFC 1874, XML
document types at a minimum cost, using existing frameworks for
media type registration. The use of a suffix convention is intended MIME entities contain
information to avoid interference with be parsed and processed by the existing MIME type structures.

As recipient's XML development continues
system. These entities may contain and such systems may permit
explicit system level commands to develop, new be executed while processing the
data. To the extent that an XML document types are
appearing rapidly. Many system will execute arbitrary
command strings, recipients of these XML document types would benefit
from the identification possibilities of a more specific MIME media
type than text/xml or application/xml can provide, and entities may be a risk. In
general, it is likely
that many new media types for XML-based document types will may be
registered in the near and ongoing future.

While possible to specify commands that perform
unauthorized file operations or make changes to the benefits display
processor's environment that affect subsequent operations.

In general, any information stored outside of specific MIME types for particular types the direct control of
XML documents are significant, all XML documents share common
structures
the user -- including CSS style sheets, XSL transformations, entity
declarations, and syntax that make possible common processing.

Some areas where 'generic' processing is useful include:

o Browsing - An XML browser DTDs -- can display any XML document with be a
provided CSS[12] source of insecurity, by either
obvious or XSLT[19] subtle means. For example, a tiny "whiteout attack"
modification made to a "master" style sheet, whatever sheet could make words in
critical locations disappear in user documents, without directly
modifying the vocabulary
of that document.

o Editing - Any XML editor can read, modify, and save any XML
document.

o Fragment identification - XPointers[16] can work with any XML
document, whatever vocabulary it uses and whether user document or not the stylesheet it uses
XPointer for its own fragment identification. [Editor's note: references. Thus,
the
use security of non-XPointer fragment identifiers by XML vocabularies like
SVG and SMIL requires further discussion.]

o Hypertext Linking - XLink[17] hypertext linking is designed to
connect any XML documents, regardless document is vitally dependent on all of vocabulary.

o Searching - Search engines, agents, the
documents recursively referenced by that document.

The entity lists and XML-oriented query tools
should be able DTDs for XHTML 1.0[XHTML], for instance, are
likely to read XML documents be a commonly used set of information. Many developers
will use and extract trust them, few of whom will know much about the content and
names level
of elements and attributes even if they 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 ignorant of fairly
obvious, but more sophisticated tricks, like changing attributes
from being optional to required, can be difficult to track down.
Perhaps the
particular vocabulary used most dangerous option available to crackers is
redefining default values for elements and attributes.

o Storage - XML-oriented storage systems, which keep XML documents
internally in attributes: e.g., if developers have
relied on defaulted attributes for security, a parsed form, should similarly relatively small
change might expose enormous quantities of information.

Apart from the structural possibilities, another option, "entity
spoofing," can be able used to process,
store, insert text into documents, vandalizing
and recreate any XML document.

When a new media type is introduced for perhaps conveying an XML-based format, 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

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name of the media type should end with "-xml". This convention will
allow applications that can process XML generically to detect that
the MIME April 2000

entity is supposed to be an XML document, verify this
assumption by invoking some XML processor, and then process the XML
document accordingly. Applications may match for types that
represent XML entities by comparing the subtype to the pattern
*/*-xml.

XML-generic processing is not always appropriate for XML-based media
types. For example, some such media types may require fragment
identifiers different from XPointer. By *not* following the naming
convention */*-xml, used, such media types can avoid XML-generic
processing.

The registration process for these media types is described in RFC
2048[7]. The registrar for the IETF tree will enforce this rule for
all XML-based media types created in as by inserting the IETF tree. Registrars for
other trees should follow this convention Communist Manifesto in order to ensure maximum
interoperability
every occurrence of their XML-based documents. Similarly, media
subtypes that do not represent XML MIME entities should &mdash;.

Use of the digital signatures work currently underway by the xmldsig
working group may eventually ameliorate the dangers of referencing
external documents not be
allowed to register with a -xml suffix.

The suffix approach allows under one's own control.

Use of XML document types is expected to be identified
within any subtree. The vendor subtree, 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 likely to
include using XML for document metadata, and a large number new
effort has begun which is considering use of XML-based document types. By using XML for medical
information. Other groups view XML as a
suffix, rather 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 setting up XML library metadata. Similarly, use of XML as a separate subtree, those types
parameter marshalling syntax necessitates a case by case security
review.

XML may
remain in also have some of the same location security concerns as plain text.
Like plain text, XML can contain escape sequences which, 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 tree of MIME types
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 they
would 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 occupied had they not been based on XML.

The optional charset parameter may keys whose output, when pressed, can be used with media types
following these conventions as described in this document for
text/xml and application/xml.
changed by sending the display processor a character sequence. If an XML-based media type
this is under possible the display of a text top-level type, object containing such
character sequences could reprogram keys to perform some illicit or
dangerous action when the charset parameter key is authoritative and subsequently pressed by the default value is "US-ASCII". If an XML-based media type is
under other top-level types, 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 charset parameter ability to
program keys should be blocked either by filtering or by disabling
the ability to program keys entirely.

Note that it is authoritative
and there are no default values. MIME processors which are not also possible to construct XML
processors should not assume a default charset, while conforming documents which make
use of what XML
processors MUST follow terms "entity references" (using the requirements in section 4.3.3 of XML
1.0[10]. The use meaning of
the charset parameter is STRONGLY RECOMMENDED,
since term "entity", which differs from the MIME definition of this information can be used
term), to construct repeated expansions of text. Recursive

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expansions are prohibited by [XML] and XML processors are required
to determine
authoritatively detect them. However, even non-recursive expansions may cause
problems with the charset finite computing resources of the XML MIME entity.

, computers, if they
are performed many times.

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References

[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/>.

[IOTP] Burdett, D., "Internet Open Trading Protocol - IOTP
Version 1.0", draft-ietf-trade-iotp-v1.0-protocol-07.txt
(work in progress).

[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", RFC 821,
August 1982.

[RFC0977] Kantor, B. and P. Lapsley, "Network News Transfer
Protocol", RFC 977, Februrary 1986.

[RFC1557] Choi, U., Chon, K. and H. Park, "Korean Character
Encoding for Internet Messages", RFC 1557, December 1999

7. Examples

The examples below give the value of the Content-type MIME header 1993.

[RFC1652] Klensin, J., Freed, N., Rose, M., Stefferud, E. and the XML declaration (which includes the encoding declaration)
inside the XML MIME entity. For UTF-16 examples, the Byte Order
Mark character is denoted as "{BOM}", D.
Crocker, "SMTP Service Extension for 8bit-MIMEtransport",
RFC 1652, July 1994.

[RFC1874] Levinson, E., "SGML Media Types", RFC 1874, December 1995.

[RFC2045] Freed, N. and the XML declaration is
assumed to come at the beginning N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of the XML MIME entity, immediately
following the BOM. Note that other MIME headers may be present, Internet Message
Bodies", RFC 2045, November 1996.

[RFC2046] Freed, N. and
the XML MIME entity may contain other data in addition to the N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
November 1996.

[RFC2048] Freed, N., Klensin, J. and J Postel, "Multipurpose
Internet Mail Extensions (MIME) Part Four: Registration

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Internet-Draft XML
declaration; the examples focus on the Content-type header Media Types April 2000

Procedures", RFC 2048, November 1996.

[RFC2060] Crispin, M., "Internet Message Access Protocol - Version
4rev1", RFC 2060, December 1996.

[RFC2077] Nelson, S.D., Parks, C. and the
encoding declaration Mitra, "The Model Primary
Content Type for clarity.

7.1 text/xml with UTF-8 Charset

Content-type: text/xml; charset="utf-8"

<?xml version="1.0" encoding="utf-8"?>

This is the recommended charset value Multipurpose Internet Mail Extensions",
RFC 2077, January 1997.

[RFC2119] Bradner, S., "Key words for use with text/xml. Since
the charset parameter is provided, MIME in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC2130] Weider, C., Cecilia Preston, C., Simonsen, K.,
Alvestrand, H., Atkinson, R., Crispin, M. and XML processors must
treat the enclosed entity as UTF-8 encoded.

If sent using a 7-bit transport (e.g. SMTP), P Svanberg,
"The Report of the XML entity must use IAB Character Set Workshop held 29
February - 1 March, 1996", RFC 2130, April 1997.

[RFC2279] Yergeau, F., "UTF-8, a content-transfer-encoding transformation format of either quoted-printable or base64.
For ISO
10646", RFC 2279, January 1998.

[RFC2396] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax.", RFC 2396,
August 1998.

[RFC2413] Weibel, S., Kunze, J., Lagoze, C. and M. Wolf, "Dublin
Core Metadata for Resource Discovery", RFC 2413,
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", RFC 2518, 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", RFC 2616, June 1999.

[RFC2703] Klyne, G., "Protocol-independent Content Negotiation
Framework", RFC 2703, September 1999.

[RFC2781] Hoffman, P. and F. Yergeau, "UTF-16, 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.

7.2 text/xml with UTF-16 Charset

Content-type: text/xml; charset="utf-16"

{BOM}<?xml version='1.0' encoding='utf-16'?>

This is possible only when the encoding of ISO
10646", RFC 2781, Februrary 2000.

[SGML] International Standard Organization, "Information
Processing -- Text and Office Systems -- Standard
Generalized Markup Language (SGML)", ISO 8879, October

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Internet-Draft XML MIME entity is transmitted via
HTTP, which uses a MIME-like mechanism Media Types April 2000

1986.

[SVG] Ferraiolo, J, "Scalable Vector Graphics (SVG)", World
Wide Web Consortium Working Draft SVG, August 1999,
<http://www.w3.org/TR/SVG>.

[UML] Object Management Group, "OMG Unified Modeling Language
Specification, Version 1.3", OMG Specification
ad/99-06-08, June 1999, <http://www.omg.org/uml/>.

[XBase] Marsh, J., "XML Base (XBase)", World Wide Web Consortium
Working Draft xmlbase, February 2000,
<http://www.w3.org/TR/xmlbase>.

[XHTML] Pemberton, S and et al, "XHTML 1.0: The Extensible
HyperText Markup Language", World Wide Web Consortium
Recommendation xhtml1, December 1999,
<http://www.w3.org/TR/xhtml1>.

[XLink] DeRose, S., Maler, E., Orchard, D. and is a binary-clean
protocol, hence does not perform CR B. Trafford, "XML
Linking Language (XLink)", World Wide Web Consortium
Working Draft xlink, July 1999,
<http://www.w3.org/TR/xlink/>.

[XML] Bray, T, Paoli, J and LF transformations C.M. Sperberg-McQueen, "Extensible
Markup Language (XML) 1.0", World Wide Web Consortium
Recommendation REC-xml, February 1998,
<http://www.w3.org/TR/REC-xml>.

[XPtr] DeRose, S., Daniel Jr., R. and
allows NUL octets. This differs from typical text MIME type
processing (see section 19.4.1 of RFC 2616[13]) for details).

Since HTTP is binary clean, no content-transfer-encoding is
necessary.

7.3 text/xml with ISO-2022-KR Charset

Content-type: text/xml; charset="iso-2022-kr"

<?xml version="1.0" encoding='iso-2022-kr'?> E. Maler, "XML Pointer
Language (XPointer)", World Wide Web Consortium Working
Draft xptr, July 1999, <http://www.w3.org/TR/xptr>.

[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)
Bridge Takatsu 201, 7-23, Sakado 3-chome, Takatsu-ku
Kawasaki-shi, Kanagawa-ken 213-0012
Japan

Phone: +81-44-833-5233
EMail: mura034@attglobal.net

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This example shows text/xml with a Korean charset (e.g., Hangul)
encoded following the specification in RFC 1557[3]. Since April 2000

Simon St.Laurent
1259 Dryden Road
Ithaca, New York 14850
USA

EMail: simonstl@simonstl.com
URI: http://www.simonstl.com/

Daniel Kohn
1445 120th Avenue NE
Bellevue, Washington 98005
USA

Phone: +1-425-602-6222
EMail: dan@dankohn.com
URI: http://www.dankohn.com/

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Appendix A. Why Use the
charset parameter is provided, '|xml' Suffix for XML-Based MIME and XML processors must treat Types?

Although the enclosed entity as encoded per RFC 1557[3].

Since ISO-2022-KR has been defined to use only 7 bits of data, no
content-transfer-encoding is necessary with any transport.

7.4 text/xml with Omitted Charset

Content-type: text/xml

{BOM}<?xml version="1.0" encoding="utf-16"?>

This example shows text/xml with a suffix was not considered as part of the charset parameter omitted. In
this case,
original MIME and XML processors must assume the charset architecture, this choice is
"us-ascii", the default charset value for text media types specified
in RFC 2046[6]. The default of "us-ascii" holds even if considered to provide the text/xml
entity is transported using HTTP.

Omitting
most functionality with the charset parameter is NOT RECOMMENDED least potential for text/xml. For
example, even if the contents of the XML MIME entity are UTF-16 or
UTF-8, interoperability
problems or lack of future extensibility. The alternatives to the XML MIME entity has an explicit encoding declaration,
XML
'|xml' suffix and MIME processors must assume the charset is "us-ascii".

7.5 application/xml with UTF-16 Charset

Content-type: application/xml; charset="utf-16"

{BOM}<?xml version="1.0"?>

This is a recommended charset value reason for its selection are described below.

A.1 Why not just use with application/xml.
Since the charset parameter is provided, MIME text/xml or application/xml and let the XML processors
must treat
processor dispatch to the enclosed entity as UTF-16 encoded.

If sent using a 7-bit transport (e.g., SMTP), correct application based on the XML MIME entity
must be encoded in quoted-printable or base64. For a binary clean
transport (e.g., HTTP) or an 8-bit clean transport (e.g., 8BITMIME
ESMTP or NNTP), no content-transfer-encoding is necessary.

7.6 application/xml with ISO-2022-KR Charset

Content-type: application/xml; charset="iso-2022-kr"

<?xml version="1.0" encoding="iso-2022-kr"?>

This example shows
referenced DTD?

text/xml and application/xml with a Korean charset (e.g.,
Hangul) encoded following the specification remain useful in many situations,
especially for document-oriented applications that involve combining
XML with a stylesheet in RFC 1557[3]. Since order to present the charset parameter data. However, XML is provided, MIME
also used to define entirely new data types, and XML 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. Although extra functionality
is available for MIME processors must

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treat the enclosed entity processors,
XML-based media types -- even when treated as encoded per RFC 1557[3], independent 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
whether the XML MIME entity has an internal encoding declaration
(this example does show such a declaration, which agrees with the
charset parameter).

Since ISO-2022-KR has been defined to type, use only 7 bits of data, no
content-transfer-encoding is necessary with any transport.

7.7 text/xml or
application/xml with Omitted Charset to label discrete media types will hinder correct
dispatching and UTF-16 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 entity

Content-type: application/xml

{BOM}<?xml version='1.0'?>

For this example, 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 MIME entity begins with 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 BOM. Since large number of XML-based document types. By using a
suffix, rather than setting up a separate subtree, those types may
remain in the
charset has same location in the tree of MIME types that they
would have occupied had they not been omitted, based on XML.

A.3 Why not create a conforming XML processor follows 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
requirements 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 1.0[10], section 4.3.3. Specifically, the to

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processor reads Media Types April 2000

describe its syntax. The two aspects of the BOM, and thus knows deterministically that media type are
completely orthogonal.

XML-based data types will most likely be registered in ALL top-level
categories (e.g., application/mathml|xml[MathML],
model/uml|xml[UML], image/svg|xml[SVG].

A.4 Why not just have the
charset encoding is UTF-16.

An XML-unaware MIME processor should make no assumptions about 'sniff' the
charset of the XML MIME entity.

7.8 application/xml with Omitted Charset and UTF-8 Entity

Content-type: application/xml

<?xml version='1.0'?>

In this example, content to
determine whether it is XML?

Rather than explicitly labeling XML-based media types, the charset parameter has been omitted, processor
could look inside each type and there 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 BOM. Since there way of
determining whether a file is no BOM, the XML processor follows the
requirements in section 4.3.3, except to fetch it and optionally check. The
same issue applies the mechanism
described in appendix F (which is non-normative) some IMAP4[RFC2060] mail applications, where
the client first fetches the MIME type as part of XML 1.0[10] the message
structure and then decides whether to
determine fetch the charset encoding of UTF-8. The XML entity does not
contain an encoding declaration, but since MIME entity.
Requiring these fetches just to determine whether the encoding is UTF-8,
this MIME type is still
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 conforming
document under certain unpreventable circumstances. (E.g., the XML MIME entity.

An XML-unaware MIME processor should make no assumptions about
declaration, comments, and processing instructions can occupy space
before the
charset 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 entity.

7.9 application/xml with Omitted Charset and Internal Encoding
Declaration

Content-type: application/xml

<?xml version='1.0' encoding="ISO-10646-UCS-4"?>

In this 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 charset parameter has been omitted,
media subtype, and there
is no BOM. 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 XML MIME entity does have an encoding

,
architecture, are never invariant across all instantiations of a
media type.

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declaration inside the XML April 2000

More practically, very few if any MIME entity which specifies the entity's
charset. Following the requirements in section 4.3.3, dispatchers and optionally
applying other MIME
agents support dispatching off of a parameter. While MIME agents on
the mechanism described receiving side will need to be updated in appendix F (non-normative) of either case to support
(or fall back to) generic XML 1.0[10], processing, it has been suggested that
it is easier to implement this functionality when acting off of the </section> XML processor determines
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 charset
encoding simplest case, of a user with neither
knowledge of the XML nor an XML-capable MIME entity (in this example, UCS-4).

An XML-unaware dispatcher. In that case,
the user's MIME processor dispatcher is likely to dispatch the content to an
XML processing application when the correct default behavior should make no assumptions about
be to dispatch the
charset of content to the XML MIME entity.

7.10 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 application responsible for the recommended charset value
content type (e.g., an ecommerce engine for use with
text/xml-external-parsed-entity. Since [IOTP]).

Note that even if the charset parameter is
provided, MIME user had already installed the appropriate
application (e.g., the ecommerce engine), and XML processors must treat that installation had
updated the enclosed entity MIME registry, many operating system level MIME
registries such as
UTF-8 encoded.

If sent using .mailcap in Unix and HKEY_CLASSES_ROOT in Windows
do not currently support dispatching off a 7-bit transport (e.g. SMTP), parameter, and cannot
easily be upgraded to do so. And, even if the XML 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.

7.11 application/xml-external-parsed-entity with UTF-16 Charset

Content-type: application/xml-external-parsed-entity;
charset="utf-16"

{BOM}<?xml?>

This is operating system were
upgraded to support this, each MIME dispatcher would also separately
need to be upgraded.

A.7 How about a recommended charset value for use with
application/xml-external-parsed-entity. Since the charset new superclass MIME parameter that is provided, defined to apply
to all MIME and XML processors must treat types (e.g., Content-Type: application/iotp;
$superclass=xml)?

This combines the enclosed entity
as UTF-16 encoded. problems of Appendix A.5 and Appendix A.6.

If sent using the sender attaches an image/svg|xml file to a 7-bit transport (e.g., SMTP) or message and
includes the instructions "Please copy the French text on the road
sign", someone with an 8-bit clean
transport (e.g., 8BITMIME ESMTP or NNTP), XML-aware MIME client and an XML browser but
no support for SVG can still probably open the XML MIME entity 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 encoded in quoted-printable or base64. For a binary clean
transport (e.g., HTTP), no content-transfer-encoding is necessary.

7.12 application/xml-dtd

Content-type: application/xml-dtd; charset="utf-8"

<?xml version="1.0" encoding="utf-8"?>

, able to interoperate
with those receiving applications.

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Charset "utf-8" is April 2000

A.8 What about adding a recommended charset value for use with
application/xml-dtd. Since the charset 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 provided, 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 XML processors must treat receiver to be upgraded, and it will also
fail in many cases (e.g., web hosting to an outsourced server),
where the enclosed entity as UTF-8 encoded.

7.13 application/mathml-xml

Content-type: application/mathml-xml

<?xml version="1.0" ?>

MathML documents are XML documents whose content describes
mathematical information, as described by MathML 1.01[15]. As 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
format based on XML, MathML documents should use conneg tag instead (e.g., accept-features:
(syntax=xml))?

When the -xml suffix
convention in 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.

Also, note that adding a content-type parameter doesn't work with
conneg either, since conneg only deals with media types, not their
parameters. This is another illustration of the limits of parameters
for MIME content-type identifier.

7.14 application/XSLT-xml

Content-type: application/XSLT-xml

<?xml version="1.0" ?>

Extensible Stylesheet Language (XSLT) documents are XML documents
whose dispatchers.

A.11 How about a third-level content-type, such as text/xml/rdf?

MIME explicitly defines two levels of content describes stylesheets type, the top-level
for other XML documents, as
described by XSLT[19]. As a format based on XML, XSLT documents
should use the -xml suffix convention kind of content and the second-level for the specific media
type. [RFC2048] extends this in their MIME content-type
identifier.

7.15 application/rdf-xml

Content-type: application/rdf-xml

<?xml version="1.0" ?>

RDF documents identified an interoperable way by using this MIME
prefixes to specify separate trees for IETF, vendor, and personal
registrations. This specification also extends the two-level type are XML documents
whose content describes mathematical information, as described by
RDF[11]. RDF documents that use a format based on XML should use
using the
-xml suffix convention in their MIME content-type identifier.

7.16 image/svg-xml

Content-type: image/svg-xml

<?xml version="1.0" ?>

Scalable Vector Graphics (SVG) documents '|xml' suffix. In both cases, processors that are XML documents whose
content describes graphical information, unaware
of these later specifications treat them as described by SVG[18]. As opaque and continue to
interoperate. By contrast, adding a format based on XML, SVG documents should use third-level type would break the -xml suffix
convention in their
current MIME content-type identifier.

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8. Revision History

draft-murata-00: Application/xml-dtd, a naming convention (*/*-xml),
and examples (application/mathml-xml, application/XSLT-xml,
application/rdf-xml, and image/svg-xml) are added.

draft-murata-01: When text/xml is more appropriate than
application/xml architecture and vice versa.

draft-murata-02: Replaced "(e.g., ESMTP, 8BITMIME, or NNTP)" with
"(e.g., 8BITMIME ESMTP or NNTP)"; transcoding without revising
encoding declarations cause numerous interoperability
failures.

A.12 What is mentioned; the choice of "US-ascii" as the
default is explained. text/xml-external-parsed-entity semantic difference between application/foo and
application/xml-external-parsed-entity
application/foo|xml?

MIME processors that are added. Examples unaware of these
two media types are added (7.10 and 7.11). References are updated.

, XML will treat the '|xml' suffix
as completely opaque, so it is essential that no extra semantics be

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References

[1] International Standard Organization, "Information Processing --
Text and Office Systems -- Standard Generalized Markup Language
(SGML).", ISO 8879, October 1986.

[2] International Standard Organization/International
Electrotechnical Commission, "Information Technology -
Universal Multiple- Octet Coded Character Set (UCS) - Part 1:
Architecture and Basic Multilingual Plane. Several amendments
and technical corrigenda have been published up April 2000

assigned to now. Other
amendments are currently at various stages of
standardization.", ISO/IEC 10646, May 1993.

[3] Choi, U., Chon, K. its presence. Therefore, application/foo and H. Park, "Korean Character Encoding
application/foo|xml SHOULD be treated as completely independent
media types. Although, for
Internet Messages", RFC 1557, December 1993.

[4] Levinson, E., "SGML Media Types", RFC 1874, December 1995.

[5] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format example, text/calendar|xml could be an
XML version of Internet Message Bodies",
RFC 2045, November 1996.

[6] Freed, N. text/calendar[RFC2445], it is possible that this
(hypothetical) new media type would include new semantics as well as
new syntax, and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046, November
1996.

[7] Freed, N., Klensin, J. in any case, there would be many applications that
support text/calendar but had not yet been upgraded to support
text/calendar|xml.

A.13 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 J Postel, "Multipurpose Internet
Mail Extensions (MIME) Part Four: Registration Procedures", RFC
2048, November 1996.

A.14 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 in RFCs the suffix so as not
to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.

[9] Yergeau, F., "UTF-8, a transformation format curtail the options of ISO 10646", RFC
2279, January 1998.

[10] Bray, T, Paoli, J and C.M. Sperberg-McQueen, "Extensible
Markup Language (XML) 1.0", World Wide Web Consortium
Recommendation REC-xml-19980210.
http://www.w3.org/TR/1998/REC-xml-19980210, February 1998.

[11] Lassila, O. and R.R. Swick, "Resource Description Framework
(RDF) Model and Syntax Specification", World Wide Web
Consortium Recommendation REC-rdf-syntax-19990222.
http://www.w3.org/TR/1999/REC-rdf-syntax-19990222, February
1999.

[12] Bos, B., Lie, H.W., Lilley, C. future users and I. Jacobs, "Cascading Style

, et. al. Expires May 31, 2000 [Page 27]

Internet-Draft developers.

Whether the inventors of a media type, today, design it for dispatch
to generic XML Media Types December 1999

Sheets, level 2 (CSS2) Specification", World Wide Web
Consortium Recommendation REC-CSS2-19980512
http://www.w3.org/TR/1998/REC-CSS2-19980512, May 1998.

[13] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., Masinter,
L., Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol
-- HTTP/1.1", RFC 2616, June 1999.

[14] processing machinery (and most won't) is not the
critical issue. The Unicode Consortium, "The Unicode Standard, Version 3.0
(ISBN 0-201-61633-5)", September 1999.

[15] Ion, P. 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 R. Miner, "Mathematical Markup Language (MathML)
1.01", World Wide Web Consortium Recommendation
REC-MathML-19980407; revised 19990707.
http://www.w3.org/1999/07/REC-MathML-19990707, July 1999.

[16] DeRose, S. 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 R. Daniel Jr., "XML Pointer Language
(XPointer)", World Wide Web Consortium Working Draft.
http://www.w3.org/1999/07/WD-xptr-19990709, July 1999.

[17] DeRose, S., Orchard, D. interoperability now and B. Trafford, "XML Linking Language
(XLink)", World Wide Web Consortium Working Draft
WD-xlink-19990726 http://www.w3.org/1999/07/WD-xlink-19990726,
July 1999.

[18] Ferraiolo, J, "Scalable Vector Graphics (SVG)", World Wide Web
Consortium Working Draft.
http://www.w3.org/1999/08/WD-SVG-19990812/, August 1999.

[19] Clark , J., "XSL Transformations (XSLT) Version 1.0", World
Wide Web Consortium Recommendation REC-xslt-19991116.
http://www.w3.org/TR/1999/REC-xslt-19991116, November 1999.

[20] http://www.w3.org/

Authors' Addresses

, in the future. So, the
conservative approach is to include the '|xml' suffix.

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MURATA Makoto (FAMILY Given)
Fuji Xerox Information Systems
KSP 9A7, 2-1, Sakado 3-chome, Takatsu-ku
Kawasaki-shi, Kanagawa-ken 213-0012
Japan

Phone: +81-44-812-7230
Fax: +81-44-812-7231
EMail: mura034@attglobal.net
URI: http://www.fxis.co.jp/DMS/sgml/

Simon St.Laurent

126 Birchwood Drive #2
Ithaca, New York 14850
US

EMail: simonstl@simonstl.com
URI: http://www.simonstl.com/

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Appendix A. Acknowledgement B. Acknowledgements

Chris Newman and Yaron Y. Goland both contributed content to the
security considerations section of this document. In particular,
some text in the security considerations section is copied verbatim
from work in progress, draft-newman-mime-textpara-00, by permission
of the author. Chris Newman additionally contributed content to the
encoding considerations sections. Dan Connolly contributed content
discussing when to use text/xml. Discussions with Ned Freed and Dan
Connolly helped refine the author's authors' understanding of the text media
type; feedback from Larry Masinter was also very helpful in
understanding media type registration issues.

Members of the W3C XML Working Group and XML Special Interest group
have made significant contributions to this document, and the
authors would like to specially recognize James Clark, Martin
Duerst, Rick Jelliffe, Gavin Nicol for their many thoughtful
comments.

Ned Freed was particularly helpful in evaluating how the '|xml'
suffix interacted with the MIME architecture as compared to
alternative proposals.

David Megginson's presentation to XTech 2000 was instrumental in
raising XML security concerns within the XML community. The
description of the problems of relying on external documents are
based on his examples.

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Appendix C. Revision History

[To be deleted before publication.]

draft-murata-00: Application/xml-dtd, a naming convention (*/*|xml),
and examples (application/mathml|xml, application/xslt|xml,
application/rdf|xml, and image/svg|xml) are added.

draft-murata-01: When text/xml is more appropriate than
application/xml and vice versa.

draft-murata-02: Replaced "(e.g., ESMTP, 8BITMIME, or NNTP)" with
"(e.g., 8BITMIME ESMTP or NNTP)"; transcoding without revising
encoding declarations is mentioned; the choice of "us-ascii" as the
default is explained

draft-murata-03: fragment identifiers for text/xml and
application/xml are escaped XPointers (section 6); the base URI may
be embedded in text/xml, application/xml,
text/xml-external-parsed-entity, or
application/xml-external-parsed-entity (section 7); utf-16le and
utf-16be are mentioned (sections 5 and 9); appendix comparing
alternatives to '|xml' suffix added; added security concerns; Lots
of minor editing.

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Acknowledgement

Funding for the RFC editor function is currently provided by the
Internet Society.

Murata, et. al. Expires May 31, September 30, 2000 [Page 31] 43]

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