rfc3023.txt

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   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, as described in Section 7.1, in
   order to enhance interoperability.

   An XML document labeled as text/xml or application/xml might contain
   namespace declarations, stylesheet-linking processing instructions
   (PIs), schema information, or other declarations that might be used
   to suggest how the document is to be processed.  For example, a
   document might have the XHTML namespace and a reference to a CSS
   stylesheet.  Such a document might be handled by applications that
   would use this information to dispatch the document for appropriate
   processing.




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3.1 Text/xml Registration

   MIME media type name: text

   MIME subtype name: xml

   Mandatory parameters: none

   Optional parameters: charset

      Although listed as an optional parameter, the use of the charset
      parameter is STRONGLY RECOMMENDED, since this information can be
      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" [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"[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[ISO8859] 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 that the charset parameter is
      authoritative.  First, some MIME processing engines do transcoding
      of MIME bodies of the top-level media type "text" without
      reference to any of the internal content.  Thus, it is possible
      that some agent might change text/xml; charset="iso-2022-jp" to
      text/xml; charset="utf-8" without modifying the encoding
      declaration of an XML document.  Second, text/xml must be



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      compatible with text/plain, since MIME agents that do not
      understand text/xml will fallback to handling it as text/plain.
      If the charset parameter for text/xml were not authoritative, such
      fallback would cause data corruption.  Third, recent web servers
      have been improved so that users can specify the charset
      parameter.  Fourth, [RFC2130] specifies that the recommended
      specification scheme is the "charset" parameter.

      Since the charset parameter is authoritative, the charset is not
      always declared within an XML encoding declaration.  Thus, special
      care is needed when the recipient strips the MIME header and
      provides persistent storage of the received XML MIME entity (e.g.,
      in a file system).  Unless the charset is UTF-8 or UTF-16, 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 media type MAY be encoded as
      appropriate for the charset and the capabilities of the underlying
      MIME transport.  For 7-bit transports, data in UTF-8 MUST be
      encoded in quoted-printable or base64.  For 8-bit clean transport
      (e.g., 8BITMIME[RFC1652] ESMTP or NNTP[RFC0977]), UTF-8 does not
      need to be encoded.  Over HTTP[RFC2616], no content-transfer-
      encoding is necessary and UTF-16 may also be used.

   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.  For maximum interoperability,
      validating processors are recommended.  Although non-validating
      processors may be more efficient, they are not required to handle
      all features of XML.  For further information, see sub-section 2.9
      "Standalone Document Declaration" and section 5 "Conformance" of
      [XML].

   Published specification: Extensible Markup Language (XML) 1.0 (Second
      Edition)[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.

   Additional information:






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      Magic number(s): None.

         Although no byte sequences can be counted on to always be
         present, XML MIME entities in 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 00 6C or FF FE 3C 00 3F 00 78 00 6D
         00 6C 00 (the Byte Order Mark (BOM) followed by "<?xml").  For
         more information, see Appendix F of [XML].

      File extension(s): .xml

      Macintosh File Type Code(s): "TEXT"

   Person and email address for further information:

      MURATA Makoto (FAMILY Given) <[e-mail]>

      Simon St.Laurent <[e-mail]>

      Daniel Kohn <[e-mail]>

   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 <[e-mail]>

      Jean Paoli <[e-mail]>

      C. M. Sperberg-McQueen <[e-mail]>

      Eve Maler <[e-mail]>

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

3.2 Application/xml Registration

   MIME media type name: application

   MIME subtype name: xml

   Mandatory parameters: none





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   Optional parameters: charset

      Although listed as an optional parameter, the use of the charset
      parameter is STRONGLY RECOMMENDED, since this information can be
      used by XML processors to determine authoritatively the charset 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" [RFC2279] and "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 contingency.  However, MIME processors
      that are not XML processors SHOULD NOT assume a default charset if
      the charset parameter is omitted from an application/xml entity.

      There are several reasons that the charset parameter is
      authoritative.  First, recent web servers have been improved so
      that users can specify the charset parameter.  Second, [RFC2130]
      specifies that the recommended specification scheme is the
      "charset" parameter.

      On the other hand, it has been argued that the charset parameter
      should be omitted and the mechanism described in Appendix F of
      [XML] (which is non-normative) should be solely relied on.  This
      approach would allow users to avoid configuration of the charset
      parameter; an XML document stored in a file is likely to contain a
      correct encoding declaration or BOM (if necessary), since the
      operating system does not typically provide charset information
      for files.  If users would like to rely on the encoding
      declaration or BOM and to hide charset information from protocols,
      they may determine not to use the parameter.

      Since the charset parameter is authoritative, the charset is not
      always declared within an XML encoding declaration.  Thus, special
      care is needed when the recipient strips the MIME header and
      provides persistent storage of the received XML MIME entity (e.g.,
      in a file system).  Unless the charset is UTF-8 or UTF-16, the
      recipient SHOULD also persistently store information about the
      charset, perhaps by embedding a correct XML encoding declaration
      within the XML MIME entity.




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   Encoding considerations: This media type MAY be encoded as
      appropriate for the charset and the capabilities of the underlying
      MIME transport.  For 7-bit transports, data in either UTF-8 or
      UTF-16 MUST be encoded in quoted-printable or base64.  For 8-bit
      clean transport (e.g., 8BITMIME[RFC1652] ESMTP or NNTP[RFC0977]),
      UTF-8 is not encoded, but the UTF-16 family MUST be encoded in
      base64.  For binary clean transports (e.g., HTTP[RFC2616]), no
      content-transfer-encoding is necessary.

   Security considerations: See Section 10.

   Interoperability considerations: Same as Section 3.1.

   Published specification: Same as Section 3.1.

   Applications which use this media type: Same as Section 3.1.

   Additional information: Same as Section 3.1.

   Person and email address for further information: Same as Section
      3.1.

   Intended usage: COMMON

   Author/Change controller: Same as Section 3.1.

3.3 Text/xml-external-parsed-entity Registration

   MIME media type name: text

   MIME subtype name: xml-external-parsed-entity

   Mandatory parameters: none

   Optional parameters: charset

      The charset parameter of text/xml-external-parsed-entity is
      handled the same as that of text/xml as described in Section 3.1.

   Encoding considerations: Same as Section 3.1.

   Security considerations: See Section 10.

   Interoperability considerations: XML external parsed entities are as
      interoperable as XML documents, though they have a less tightly
      constrained structure and therefore need to be referenced by XML
      documents for proper handling by XML processors.  Similarly, XML
      documents cannot be reliably used as external parsed entities



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      because external parsed entities are prohibited from having
      standalone document declarations or DTDs.  Identifying XML