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Re: ISSUE-117 (about-on-HTML): Consider disallowing @about on <html> [RDFa 1.1 in HTML5]

From: Mark Birbeck <mark.birbeck@webbackplane.com>
Date: Sun, 20 Nov 2011 14:27:10 +0000
Message-ID: <CANTqjMmcjSOd=SKP=N5w+qoENo_KdA2u2TfKfryGd04HBgffTg@mail.gmail.com>
To: Ivan Herman <ivan@w3.org>
Cc: Toby Inkster <tai@g5n.co.uk>, RDF Web Applications Working Group WG <public-rdfa-wg@w3.org>, sysbot+tracker@w3.org
Hi Ivan,

> The only minor issue in what you are saying is that we _do_ have a hidden default @about in <html>;
> indeed, the processing rules explicitly refer to the fact that the top element sets the subject to the
> document URI (unless explicitly said). Ie, we have some sort of a mixture here.

Right, but as described in the links I sent earlier having an implied
@about on <html> doesn't ensure complete protection of the metadata in
<head> (more on this below).


> I am not sure whether you followed the mailing list. The problem is that when moving all this to HTML5,
> very unexpected things happen simply because HTML5 is permissive and allows for a head/body
> element to be missing in the original source, but will be added to the DOM tree.

Yes, I have followed that thread, although in this case I was only
jumping in in response to you saying that you couldn't remember why we
had that feature.


> Toby, who is unbeatable in identifying such edge cases:-) has shown some horrible examples.

Only one of his many talents. ;)


> On the other hands, the (purely anecdotical) experience shows that very few users (if any) used
> the trick of putting an empty @typeof into the <head> or the <body>. Hence the proposal to drop
> these (but keeping the default @about in <html>).

I realise that the use of @typeof in that way may be an edge case, but
does that matter? I ask because I feel that the purpose of the implied
@about was not to provide extra feature, but to protect existing HTML
metadata features from suddenly changing their meaning with a minor
use of RDFa. I think that still holds; whether we think anyone will
ever put RDFa on the <head> element or not, it's just too risky to
define the rules in such a way that adding a single attribute can wipe
out the presence of metadata that might have been added to an HTML
document.

That doesn't necessarily mean that having an implied @about is the
best way to solve this problem of course.

One alternative approach might be to deem that any RDFa is ignored on
<html>, <head> and <body>, and so processing only begins /inside/
<head> and <body>. Another might be to investigate whether <link>
could be said to *always* apply to the current document, unless @about
is present on the element itself. (That would still leave the issue
unresolved for <body>, since saying that <a> always uses the current
document for its subject will negate chaining, etc.)

Regards,

Mark
Received on Sunday, 20 November 2011 14:28:28 GMT

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