Validing XHTML vs Html

[Peter Williams]

Hello,

If my html is valid XHTML accroding to http://validator.w3.org/, does
thuis mean it is also valid (4.0.1) Html?

Thanks in Advance

[Ian Rastall]

On 2 Mar 2006 02:49:28 -0800, "Peter Williams" <p8****@gmx.net > wrote:

If my html is valid XHTML accroding to http://validator.w3.org/, does
thuis mean it is also valid (4.0.1) Html?

Hi Peter. A test you could try is to make a copy of a file, change the
DOCTYPE, and then try to re-validate it.

XHTML is usually served up with the MIME type "text/html", which means
that browsers see it as HTML, and render it correctly. This is because
XHTML was designed for backwards-compatability. Another way of saying
this is that XHTML is broken HTML that happens to be broken in just
such a way that it doesn't break the page. It is not valid HTML 4.01,
though, to answer your question.

The real MIME type for XHTML is "applicatio n/xhtml+xml", which most
browsers recognize, but which Internet Explorer doesn't recognize.
Since IE commands most of the market share, and since they're not
going to accomodate this MIME type in IE 7, a lot of web designers
have gone back to HTML 4.01. I've done the same thing. I actually
learned XHTML first, and stuck with it for many years. If you use a
text editor that supports HTML Tidy, then making the conversion back
to HTML 4.01 is as simple as changing the DOCTYPE and then tidying the
page.

Ian
--
http://sundry.ws/

[Steve Pugh]

Peter Williams wrote:

If my html is valid XHTML accroding to http://validator.w3.org/, does
thuis mean it is also valid (4.0.1) Html?

Obviously the doctypes will be different - a valid HTML 4.01 document
should have a HTML 4.01 doctype and a valid XHTML 1.0 document should
have a XHTML 1.0 doctype.

But ignoring that (and the whole content-type farce), if you swapped
doctypes (or used the over ride feature in the validator) would it be
valid? Maybe.

If your XHTMLisms are confined to those that look like HTMLisms then it
will be valid.

So, you would need to have:
* No empty elements in the head (so no <link> or <meta> elements) or
anywhere else where character data can't appear.
* No boolean attributes anywhere (so no compact, readonly, disabled or
nowrap attributes).

Of course there are valid XHTMLisms that look like valid HTMLisms but
which mean something totally different in HTML (e.g. <br /> means <br>>
not <br></br>).

Steve

[David Dorward]

Steve Pugh wrote:

Peter Williams wrote: If your XHTMLisms are confined to those that look like HTMLisms then it
will be valid.

So, you would need to have:
* No empty elements in the head (so no <link> or <meta> elements) or
anywhere else where character data can't appear.
Although any of those used where character could appear would have
different meaning in HTML than in XHTML.
* No boolean attributes anywhere (so no compact, readonly, disabled or
nowrap attributes).

HTML does allow for the expanded form of boolean attributes, it just
isn't recomended.

http://www.w3.org/TR/html4/appendix/notes.html#h-B.3.4

[Andy Dingley]

Peter Williams wrote:

If my html is valid XHTML accroding to http://validator.w3.org/, does
thuis mean it is also valid (4.0.1) Html?

No, it certainly doesn't _mean_ that.

If you didn't use certain features, and you swap the doctype, then it
_may_ be valid as both.

It's not really useful to know this though. They are different and they
do need separate processing. Searching this newsgroup is probably the
best resource around on the details. If you don't _really_ understand
this, then stick with HTML 4.01

[Steve Pugh]

David Dorward wrote:

Steve Pugh wrote:

* No boolean attributes anywhere (so no compact, readonly, disabled or
nowrap attributes).

HTML does allow for the expanded form of boolean attributes, it just
isn't recomended.

http://www.w3.org/TR/html4/appendix/notes.html#h-B.3.4

Thanks, I'd never come across that before.

Steve

[Jukka K. Korpela]

Andy Dingley wrote:

If my html is valid XHTML accroding to http://validator.w3.org/, does
thuis mean it is also valid (4.0.1) Html?
No, it certainly doesn't _mean_ that.

Indeed; it means that the document _cannot_ be valid HTML 4.01.
If you didn't use certain features, and you swap the doctype, then it
_may_ be valid as both.
Well, it's not the same document any more if you swap the doctype.

Besides, a document that conforms to the XHTML specification does not
become a (valid) HTML 4.01 document just by swapping the doctype, even
if we ignore issues already discussed here. The xmlns attribute is
obligatory, though for technical reasons, it is not required as an
explicit attribute according to the DTD. (Thus, an XHTML document that
lacks the attribute is valid but incorrect, nonconforming.)

An XML declaration (<?xml ...>) at the start of document, as allowed in
XHTML, makes a document nonconforming (though not invalid) by HTML 4.01
rules.

There are also differences in content models of <script> and <style>
elements. They can be essential if you have "&" or "<" characters inside
them.
It's not really useful to know this though.

Yeah, it's just fun to get confused with this. However it _is_ an issue,
in principle at least, if you wish to author so that you serve the same
content as HTML 4.01 to some browsers and as XHTML to other browsers.

[Peter Williams]

> However it _is_ an issue, in principle at least, if you wish to author so that you serve the same content as HTML 4.01 to some browsers and as XHTML to other browsers.

This is what Im aiming at.

[Peter Williams]

I suppose my original question should have better have been phrased:

Apart form some trivialities (eg swapping DOCTYPE) correct XHTML is a
superset of correct HTML ? So that by writing correct XHTML and
avoiding anything outside the overlap (XHTML thats not part of HTML),
the result will be even more "standard" than correct HTML (ie all
elements properly closed etc)?

Or are the trivialities not so simple, so that it wouldnt be so trivial
to convert my XHTML documents to HTML, by hand via simlpe editing such
as swapping of the DOCTYPE? Are there things to be weary of here?

[Chris Beall]

Peter Williams wrote:

However it _is_ an issue, in principle at least, if you wish to author so that you serve the same content as HTML 4.01 to some browsers and as XHTML to other browsers.

This is what Im aiming at.

Peter,

How brave are you?

Back up all your files, then go to w3.org and download the appropriate
version of Amaya.

Open a file, then:

File, Show parsing errors (unless it's greyed out). Fix the errors.

File, Change the Document Type. Pick one. Let it crank a while. Then
File, Save as...

CAUTION: This code is under test. Bad Things can happen. Proceed at
your own risk.

Chris Beall