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Re: XHTML 1.0 served as text/html

From: olivier Thereaux <ot@w3.org>
Date: Wed, 6 Dec 2006 09:05:50 +0900
Message-Id: <D4E65970-B08D-4F86-B6DA-7E595B85F887@w3.org>
Cc: Ian Hickson <ian@hixie.ch>, david@djwhome.demon.co.uk, jkorpela@cs.tut.fi, karl@w3.org, link@pobox.com, www-validator <www-validator@w3.org>, www-html@w3.org
To: Philip TAYLOR <P.Taylor@Rhul.Ac.Uk>

Hello Philip,

On Dec 6, 2006, at 03:19 , Philip TAYLOR wrote:
> I was more
> than a little surprised
> it states that the (page) is "Valid XHTML 1.0 Transitional"
> without issuing even a warning that it is being served as
> text/html rather than application/xhtml+xml.

Serving XHTML 1.0 content as text/html is perfectly legit per the  
XHTML 1.0 specification, and the section 5.1 you quote. There is even  
an section on how to ensure that content served that way can be  
interpreted by legacy user-agents.

Also, as RFC2854 says, XHTML1 defines a profile of use of XHTML  
which is compatible with HTML 4.01 and which may also be labeled as  

So, there is no clear foul here.

> Now it is
> clear from Section 5.1 of
> 	http://www.w3.org/TR/xhtml1/
> that this is acceptable,

Indeed it does. I think the prose of the XHTML 1.0, in this regard,  
is imperfect, as Section 5.1 implies that the (informative) appendix  
C (compatibility guidelines) are in fact informative-except-if- 
serving as text-html. It could probably have been made a little  
clearer whether AppC is informative and applying only to some cases,  
or conditionally normative...

> yet
> 	http://www.w3.org/TR/xhtml-media-types/
> also states clearly that
> 	"application/xhtml+xml SHOULD be used for XHTML Family documents"

Let's quote the full sentence:
[[ In summary, 'application/xhtml+xml' SHOULD be used for XHTML  
Family documents, and
the use of 'text/html' SHOULD be limited to HTML-compatible XHTML 1.0  
documents. ]]

The Note also summarizes thus:

XHTML Rec says:
  * MAY text/html (but then, follow appendix C)
  * MAY application/xhtml+xml

Media Type Note says:
  * MAY use text/html
  * SHOULD use application/xhtml+xml

I don't think this is a discrepancy, rather, I assume that the Note,  
an informative set of recommended practices, pushes for the usage of  
application/xhtml+xml, because is a good idea for a number of reasons  
(no need to follow appendix C guidelines, clear XML parsing model).

> My question is therefore : should not the validator issue
> a warning when this last guideline is ignored ?

The plan I have is to have the validator issue a note, when finding  
content served as text/html and matching the doctypes for XHTML 1.0,  
suggesting to run the content through the HTML compatibility checker  
(demo'd at [1]). The validator and appendix C checker are also  
automatically put together by the unicorn tool (see [2] and demo at [3])

[1] http://qa-dev.w3.org/appc/
[2] http://www.w3.org/QA/2006/obs_framework/
[3] http://qa-dev.w3.org/unicorn/

Hopes this helps answering your questions.
olivier Thereaux - W3C - http://www.w3.org/People/olivier/
W3C Open Source Software: http://www.w3.org/Status
Received on Wednesday, 6 December 2006 00:06:00 UTC

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