Revised XML registration

Paul Grosso has very kindly shared the language that he used when
registering the SGML Open catalog (along with a tip that could save us
a few months in getting this approved).  I have spliced Paul's SGML
Open language in below with some questions for our MIME experts.



To: iana@isi.edu
cc: w3c-sgml-wg@w3.org
Subject: Registration of MIME media type text/xml

MIME media type name: text

MIME subtype name: xml

Required parameters: none

Optional parameters: charset

Here is what Paul said for SGML Open catalogs:

	For use over the Internet, a catalog may use only a single character
	repertoire.  (A character repertoire describes a set of characters,
	where a character is an atom of information.  A character repertoire 
	does not describe any of the common attributes typically associated 
	with a character such as the character's form or coded representation.
	For example, the letter capital cee is a character, it can take the 
	form C and has the US-ASCII coded representation of 67 decimal.)
	The mapping from the sequence of octets making up the message body, 
	to the sequence of characters making up the catalog, is indicated by 
	the charset parameter of the Content-Type MIME header line [RFC1521].  

	The value of the charset parameter must be one that is registered
	with IANA [RFC1700], or employ an extension-token, such as X-big10. 
	In general, it should be possible to infer the character repertoire 
	and coded character set from the name of the encoding.

	If no value is supplied, the default shall be US-ASCII.

Do we want to say the same thing?

Encoding considerations: the primary encodings are UTF-8 and UCS-2,
but other common encoding schemes such as SJIS are also allowed.
UTF-8 is the default.

Here is what Paul said for catalogs:

Encoding considerations: Some encodings of coded character sets may
                         require that an additional
                         content-transfer-encoding be applied. 

Do we want to say the same thing?

Security considerations: the security considerations associated with
text/plain apply.

Obviously just punting.  Paul has:

Security considerations: This media type contains SGML references to 
			 external object, files, and programs.  Its use
			 does present security implications due to the 
			 access of these entities by SGML systems.
			 However, these security concerns are the same as 
			 those for the operation of any SGML system and 
			 are addressed in the SGML specifications.

The same would apply to XML, right?

Interoperability considerations: the interoperability considerations
associated with text/plain apply.

Same here.  Paul said:

Interoperability considerations: The specification for this media type 
			 (see "Published specification" below) provides 
			 for extensions by allowing for other information, 
			 i.e., <keyword, argument+> pairs.  The usefulness 
			 of such other information will depend on the range 
			 of recognition of each such extension.  However, 
			 the specification indicates that a processor of 
			 this media type shall be able to process a catalog 
			 even if it does not recognize the meaning of such 
			 an extension.

The first part of this looks like it might be recyclable.

Published specification: Extensible Markup Language (XML), W3C Working
Draft 14-Nov-96 (http://www.w3.org/pub/WWW/TR/WD-xml-961114.html; also
ftp://sunsite.unc.edu/pub/sun-info/standards/xml/spec/xml.ps.gz, etc.)

A couple of people have pointed out that XML does indeed hava a
"magic number" (see below).

Additional information:

 Magic number(s): <?xml
 File extension(s): xml
 Macintosh File Type Code(s): none

Person and email address to contact for further information:

 Jon Bosak, jon.bosak@sun.com

Intended usage: COMMON

Authors/Change controllers:

 Tim Bray, tbray@textuality.com
 C. M. Sperberg-McQueen, U35395@UICVM.UIC.EDU