Quoting Sebastian Redl <sebastian.redl@getdesigned.at>:
>> DTDs are ingored, but did you ever play with XML (or XHTML) as 
>> opposed to HTML?
>> You can do all funny things you want to do. Like nesting <div> 
>> inside <span> et
>> cetera.
>
> Define "can".

The dictionary meaning. Not sure what it is unclear here...


> In XML, elements are arbitrary and have no meaning. You can nest 
> whatever you want in everything else, and the document will be 
> well-formed.

Being well-formed or not depends on more things, but that was actually 
my point.
As long as the doucment is well-formed it does not really matter what you do.


> But specific XML languages, such as XHTML, go beyond that and define 
> the document structure. A non-validating parser will accept a div 
> inside a span for XHTML, but it is invalid according to the standard 
> and all schemas, and a validating parser will reject it.

That's why I said DTDs are ignored. You shouldn't really use them in the first
place.


> The same in HTML: it's invalid, but browsers will accept it because 
> they're very forgiving. However, the results of this, especially the 
> display behaviour of showing a block element inside an inline 
> element, are undefined. You can't rely on a behaviour.

If browsers weren't forgiving the extensibility of the language would 
stop more
or less. Also, an XML/XHTML/HTML document can go in and out of being valid
dynamically, so what you're saying would have never worked in practice anyway.
The SVG WG, for one, acknowledged this.


-- 
Anne van Kesteren
<http://annevankesteren.nl/ >