Content-Document-Type: was (Re: MIME types vs. DOCTYPE)

Walter Underwood wunder at
Fri Feb 26 17:51:39 GMT 1999

I feel that Content-document-type is a poor idea. It put something
specific to XML in a generic header.

Not all clients care about the doctype. Some (like search engines)
don't need to render it. Others may just need to cache it.

If a document is XHTML, and should have a default rendering, I'd
call that a processing instruction:

  <?xhtml version="1.0" doctypes="strict, frameset">

or whatever does the job.

The objection about thin clients or palmtops not wanting to download
large files doesn't really hold water. XML will generally be the 
smallest files. Mine are almost always smaller than the corresponding
HTML. Powerpoint, PDF, JPEG -- those are big files. 

Adding an XML-specific HTTP header line makes HTTP 1.1 more complex
(shudder), and imposes an extra coding and testing burden on HTTP
implementations. Also, it does nothing for XHTML over other transports,
like SMTP or FTP.

Essentially, this is document information, not protocol information. 
It belongs in the document. To describe the document out-of-line, 
use RDF, not HTTP headers.

Pragmatically, HTTP Content-type isn't even reliable. Somebody will 
decide that Excel and XML are the same thing, and start serving 
spreadsheets as text/xml. Cell phones have to deal with that world, 
and adding things to the HTTP spec doesn't fix ignorant sysadmins. 
And lots of web servers serve application-specific files (MS Word,
Powerpoint, Excel) as application/octet-stream in order to force 
the browser to put up a save box rather than display them in the 
frame. We see this sort of stuff all the time with the search engine.

XHTML Spec comment: the spec doesn't mention application/xml. It should. 
If application/xml is never appropriate for XHTML (say, the UTF-16
encoding is forbidden), then say so.

XHTML Spec comment: Are the Strict, Transitional, and Frameset DTDs
subsets or extensions? Or neither? Is one a subset of another? These
intentions should be spelled out in the spec so that future versions
won't break them.


Walter R. Underwood
wunder at
wunder at (home) (my product)

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