Henri Sivonen <hsivonen@iki.fi> wrote:
[color=blue][color=green]
>> <pre><a><img src="image.png" alt="" /></a></pre>
>> validates as XHTML 1.0 Strict whereas
>> <pre><a><img src="image.png" alt=""></a></pre>
>> does not validate as HTML 4.01 Strict, when I used
>>
http://validator.w3.org/ for validation.[/color]
>
> XML DTDs are more limited in their expressiveness. The inability to
> express exclusions like that is one of the limitations.[/color]
The XHTML 1.0 DTD tries to overcome the limitation by using a special
content model for the <pre> element:
<!-- pre uses %Inline excluding big, small, sup or sup -->
<!ENTITY % pre.content
"(#PCDATA | a | %fontstyle; | %phrase; | %special.pre; | %misc.inline;
| %inline.forms;)*">
This won't make <pre><a><img src="image.png" alt=""></a></pre> invalid,
though, since the rules are satisfied: <pre> contains just the <a> element,
which is allowed of course, and the content model of <a> allows any inline
content, including <img>.
It would be possible, but highly impractical, to write XML syntax rules in
a manner that corresponds to the HTML rules for <pre>. You would
essentially have to duplicate a large number of syntax rules, having both
"general version" and "pre version". Besides, the whole point in those
<pre> rules is questionable. The intent is to disallow markup that might
cause font size to change or might introduce anything that is not
representable as a "character cell". Yet, allowing e.g. form fields inside
<pre> works against this idea, and sounds rather pointless.
--
Yucca,
http://www.cs.tut.fi/~jkorpela/
Pages about Web authoring:
http://www.cs.tut.fi/~jkorpela/www.html 
