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Re: "charset" is not generic to all media types [nsMediaType-3]

From: Graham Klyne <GK@ninebynine.org>
Date: Mon, 04 Feb 2002 21:26:51 +0000
Message-Id: <5.1.0.14.2.20020204210205.03872ec0@joy.songbird.com>
To: Dan Connolly <connolly@w3.org>
Cc: www-tag@w3.org
Your observation is correct -- charset is defined for subtypes of text.  It 
may be defined for other media types, but there's no mechanism for making 
one parameter be applicable to all media types.

This was an explicit design decision:  the text you quote goes on to say:
[[[
    Truly global mechanisms are best addressed, in the MIME
    model, by the definition of additional Content-* header fields.
]]]

It may be silly to define charset for some media type to mean something 
different, but there are also some media types for which a charset 
parameter would be meaningless.

#g
--

At 08:56 AM 2/4/02 -0600, Dan Connolly wrote:
>The diagram
>   http://www.w3.org/2001/04/roadmap/xml-charset.svg
>   http://www.w3.org/2001/04/roadmap/xml-charset.n3
>
>suggests that one can look for a "charset" parameter
>on any XML document in a MIME body part; i.e.
>that the semantics of parameters named "charset"
>is shared across all media types.
>
>I wondered whether that's the case, which
>earned me...
>
>"Action DC: Verify that parameter names are local
>to each MIME type."
>   -- http://lists.w3.org/Archives/Public/www-tag/2002Jan/0235
>
>Indeed...
>
>[[[
>For example, the "charset" parameter is applicable to any subtype of
>    "text", while the "boundary" parameter is required for any subtype of
>    the "multipart" media type.
>   There are NO globally-meaningful parameters that apply to all media
>   types
>  ]]]
>   -- http://www.ietf.org/rfc/rfc2045.txt
>
>Perhaps it's cost-effective to change this; after all,
>it seems silly for somebody to define a media type
>with a parameter named "charset" that means something else.
>But as it is, the algorithm in the diagram relies
>on more than the specs guarantee.
>
>--
>Dan Connolly, W3C http://www.w3.org/People/Connolly/

------------
Graham Klyne
GK@NineByNine.org
Received on Monday, 4 February 2002 16:40:26 GMT

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