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Re: xmlns in HTML5 (was: Telecon Agenda- Thursday 1500 UTC)

From: Ian Hickson <ian@hixie.ch>
Date: Fri, 17 Jul 2009 22:05:52 +0000 (UTC)
To: Toby A Inkster <tai@g5n.co.uk>, Steven Pemberton <Steven.Pemberton@cwi.nl>
Cc: RDFa list <public-rdf-in-xhtml-tf@w3.org>
Message-ID: <Pine.LNX.4.62.0907172147330.12284@hixie.dreamhostps.com>
On Fri, 17 Jul 2009, Toby A Inkster wrote:
> On 17 Jul 2009, at 12:34, Ian Hickson wrote:
> > 
> > It is literally not possible to send XHTML5 as text/html, because as 
> > soon as you label it as text/html, you are stating "it is HTML".
> As soon as Steven labels it as text/html, he is stating that it is HTML. 
> But that doesn't mean that it is HTML.

This seems somewhat meta. If you put something in an envelope and put it 
in the post, it's a piece of mail, whether it has a letterhead or not. 
Similarly, if you label something as text/html, it's an HTML document, 
whether it's conforming or not. It may not have originally been intended 
as an HTML file, but that's a quite different matter.

> My website is XHTML, but it will be served as text/html if your browser 
> seems to prefer it that way.

Given an arbitrary stream of bytes without a label, there is no way to 
determine whether it is intended to be HTML or XHTML, especially now with 
HTML5 since e.g. some of XHTML1's DOCTYPEs are valid in text/html HTML5.

So the label really is the only thing that can distinguish them.

On Fri, 17 Jul 2009, Toby A Inkster wrote:
> Further, if I serve it as text/plain so that people can see the source 
> code and learn from its wonderousness, then are they viewing HTML source 
> code or XHTML source code?

They're viewing a text/plain file. What that source supposes to be is a 
matter for the author and the reader, there is no technical answer.

On Fri, 17 Jul 2009, Steven Pemberton wrote:
> > > 
> > > Not valid, but permitted.
> > 
> > Woah. What's the difference between "valid" and "permitted"? Aren't 
> > they both synonyms of "conforming"?
> Not at all. Valid has a very well defined meaning, with respect to 
> schemata. I used 'permitted' in its English sense.

So it is permitted to write HTML4 documents that violate the HTML4 schema? 
How is that possible, given HTML4's definition of "HTML document" as "An 
HTML document is an SGML document that meets the constraints of this 
specification"? Surely if one violates the contraints, one is no longer 
writing an HTML document? I'm very confused by your position here.

> A document with extra attributes may be a valid according to some other 
> schema, but it is still permitted to send it to an HTML4 processor, 
> because the spec says so.

Where does it say so?

The sentence you quoted did not say this, it merely gave a suggested (not 
even required -- the section is explicitly non-normative!) way for user 
agents to handle a particular error condition. It's not giving authors 
permission for anything.

> > > > > "If a user agent encounters an attribute it does not recognize, 
> > > > > it should ignore the entire attribute specification (i.e., the 
> > > > > attribute and its value)." 
> > > > > http://www.w3.org/TR/html401/appendix/notes.html#notes-invalid-docs
> > 
> > > But the HTML4 spec defines a document type, and says the processor 
> > > for that document type must accept certain deviations from that in 
> > > order to allow for future change. In other words the spec 
> > > anticipated that other document types would be sent in the future.
> > 
> > Sure, future compatibility is a pretty standard part of any language. 
> > But if you agree that the above quote is a statement about _user 
> > agents_, as opposed to authors, I don't understand how you then 
> > conclude that it can in any way affect document conformance (what 
> > authors are permitted to do).
> Suppose we define a new markup language, Accessible HTML, which includes 
> the role attribute and all the WAI ARIA attributes. It permits an author 
> to write a document that validates according to that new schema, and 
> send it to an HTML4 processor, with well-defined processing. The author 
> can also send it to an Accessible HTML processor, which can do extra 
> things with it, but it will still work with a legacy processor.

You didn't answer my question. I didn't ask how _another_ spec could 
override HTML4's requirements. I asked how the sentence you quoted above 
could in any way be interpreted to grant permissions to authors.

In your example, "Accessible HTML", per HTML4, defines a class of 
documents that are not "HTML documents" and that therefore are not under 
the purview of HTML4 at all. The "Accessible HTML" spec can defer to HTML4 
for all its processing rules (much like how XHTML 1.x defer to HTML4 for 
most of the non-syntax-related conformance statements), but that doesn't 
mean that HTML4 allows it. As far as I can tell, it explicitly disallows 
it and disclaims any involvement.

This is contrary to HTML5, which claims authority over any text/html 
content, valid or not, and then explicitly allows other specifications to 
adjust the conformance criteria to allow further extensions.

Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'
Received on Friday, 17 July 2009 22:06:28 UTC

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