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

From: Ivan Herman <ivan@w3.org>
Date: Sun, 20 Nov 2011 17:44:52 +0100
Cc: Toby Inkster <tai@g5n.co.uk>, RDF Web Applications Working Group WG <public-rdfa-wg@w3.org>, sysbot+tracker@w3.org
Message-Id: <A198AFEF-BFB3-493A-BA7A-72A78EA5FBA0@w3.org>
To: Mark Birbeck <mark.birbeck@webbackplane.com>

On Nov 20, 2011, at 15:27 , Mark Birbeck wrote:
[snip]
> 
> 
>> 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.
> 

Well, the problem is that we are between a rock and a hard place. I understand your argument; on the other hand, the present rules are such that unexpected triples will be generated in case no head or body element is used. In a sense, the latter is worse than the former: indeed, while I could suppose that an author knowing what @typeof means would also know what @about means, ie, it is not a big leap forward to do the right thing, the latter case is much trickier. It presupposes the knowledge though the <head> element is not in the source, the HTML5 parser _will_ put that into the DOM tree, ie, the RDFa processing has no other choice than to operate on such extended tree.

In his original mail Toby put that example as a riddle to be solved. And I miserably failed! :-( I simply did not realize or think about that additional DOM behaviour either...

Ivan

> 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
> 


----
Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
mobile: +31-641044153
FOAF: http://www.ivan-herman.net/foaf.rdf
Received on Sunday, 20 November 2011 16:42:10 GMT

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