Posted by David Dorward on 11/06/07 09:45

On Nov 5, 7:52 pm, Bone Ur <monstersquas...@yahoo.com> wrote:

> Well, I didn't know some of that, particularly that XML can be parsed
> without accessing a dtd. But xhtml "needs" a dtd, or is it just because
> of the compatibility issues with appendix c et al?

The spec requires that XHTML documents have a Doctype.

Not having a Doctype triggers Quirks mode in many browsers.

Appendix C has nothing to do with this.

> And if in the context
> of what you said there's a meaningful difference between XML and xhtml,
> the logical question is can SGML (not html) be parsed without a dtd also?

When I said 'XML', I meant "a given dialect of XML".

Given a dialect of SGML, and no DTD, it isn't possible to know which
elements have optional start tags, which have optional end tags, and
which have forbidden end tags. If we use HTML for example:

<title>foo</title>
<p>Hello, world
<div>Goodbye, world</div>

Without knowing HTML (via a DTD or otherwise), the parser has no way
to know that it needs to insert an HTML, HEAD and BODY elements, or
that the P element should end before the DIV and not after it.

> Anyway, I'm still not impressed. What's wrong with making <img
> src="my.png">Look at me.</img> the "right way to do it" and getting rid
> of the stupid "alt" attribute?

It would be nice, and HTML 4.01 has:

<object type="image/png" src="my.png">Look at me.</object>

.... but browser support is weak.

<img> is legacy from HTML 3.2 and earlier.

> that's for sure, and if compatibility is the issue which is inhibiting
> innovation, the solution is obviously to go another way. Well, it's
> obvious to me.

The problem with abandoning everything we have already is that you
have to get browser vendors to support the new thing (nobody is using
it, where's the demand?) and authors to use the new thing (the old
thing does what I want, and nothing supports the new thing). Which is
why XHTML 2 is likely to fail on the web.

--
David Dorward
http://dorward.me.uk/
http://blog.dorward.me.uk/

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