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Re: XHTML 2.0 - 3.2 Conformance Requirements (PR#7651)

From: Bjoern Hoehrmann <derhoermi@gmx.net>
Date: Fri, 27 May 2005 02:53:07 +0200
To: Shane McCarron <shane@aptest.com>
Cc: www-html-editor@w3.org, jim.ley@gmail.com, w3c-html-wg@w3.org
Message-ID: <42965d95.451341656@smtp.bjoern.hoehrmann.de>

* Shane McCarron wrote:
>I think you are misunderstanding the constraint. It is a hold-over from 
>XHTML 1.0, which could be processed as either "XML" or "HTML", depending 
>on the user agent.

In XHTML 1.0 this is a requirement for XHTML 1.0 user agents, it is not
possible for such a user agents to process XHTML documents as HTML. It
is also not possible for HTML user agents to process XHTML documents as
HTML either, HTML and XHTML are not compatible at all. So indeed, the
requirement was inappropriate for XHTML 1.0 aswell, as I've pointed out
in http://lists.w3.org/Archives/Public/www-html-editor/2001OctDec/0084

  |     3. When a user agent processes an XHTML document as generic
  |        XML, it shall only recognize attributes of type ID (e.g.
  |        the id attribute on most XHTML elements) as fragment
  |        identifiers.
  
  This item should be removed, [...]

I'm still waiting for the response that formally addresses the issues
raised in that message by the way...

>This is readily achievable today through the use of a stylesheet, should 
>you wish to suppress the PCDATA content of an element (e.g., display: 
>none or visibility: hidden).  The working group has debated introducing 
>an attribute that would mean "do not present the content of this 
>element".  There was no consensus for this proposal, as far as I know.

XHTML 2.0 user agents are not required to support CSS and even if they
support CSS, this method does not actually work. Consider

  <html xmlns="http://www.w3.org/2002/06/xhtml2">
  <head>
    <title>...</title>
    <style>
      svg { display: none }
    </style>
  </head>
  <body>
  ...
    <svg xmlns="http://www.w3.org/2000/svg"
         version="1.2" baseProfile="tiny">
      ...
    </svg>
  ...
  </body>
  </html>

The XHTML 2.0 + SVG Tiny 1.2 user agent would likely apply the style
sheet so you would have to re-enable rendering of the SVG content in the
SVG fragment which you can't as Tiny 1.2 does not support the svg:style
element. Worse if the element is added to XHTML 2.0 like <style> and
<script> have been added to HTML, since you cannot write style sheets
that only apply if the user agent supports specific elements.

http://www.w3.org/MarkUp/Forms/2002/Examples/spec-examples/ has lots
of examples for the latter, just imagine XForms won't be part of XHTML
2.0, you would get all sorts of strange text in the documents or no
text at all if display is set to none. So we can conclude that the
proposed forward compatibility rules fail the provide the desired
functionality.

That's not surprising actually, XHTML 2.x currently uses XHTML 1.x's
"extensibility" model and XHTML 1.x uses HTML 4.01's model and the
HTML workshop http://www.w3.org/MarkUp/future/ in 1998 clearly con-
cluded that "extending HTML 4.0 would be difficult" ...
-- 
Björn Höhrmann · mailto:bjoern@hoehrmann.de · http://bjoern.hoehrmann.de
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Received on Friday, 27 May 2005 01:00:45 GMT

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