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Re: [Fwd: Using XMLNS in link/@rel]

From: Mark Nottingham <mnot@mnot.net>
Date: Fri, 27 Feb 2009 21:54:24 +1100
Cc: www-tag@w3.org, "Dan Brickley" <danbri@danbri.org>, "Ben Adida" <ben@adida.net>, RDFa <public-rdf-in-xhtml-tf@w3.org>, "XHTML WG" <public-xhtml2@w3.org>
Message-Id: <98EE693C-B02B-4E12-A505-2D16A22C1145@mnot.net>
To: Steven Pemberton <steven.pemberton@cwi.nl>

Hello Steven,

On 27/02/2009, at 9:06 PM, Steven Pemberton wrote:

> On Fri, 27 Feb 2009 10:31:57 +0100, "Mark Nottingham"  
> <mnot@mnot.net> said:
>> Creative Commons just released a new spec:
>>   http://wiki.creativecommons.org/Ccplus
>> that has markup in this form:
>>   <a xmlns:cc="http://creativecommons.org/ns#"
>> rel="cc:morePermissions" href="#agreement">below</a>
>> (in HTML4, one assumes, since they don't specify XHTML, and this is
>> what the vast majority of users will presume).
> In the link you refer to they don't specify either, but I imagine  
> they mean XHTML,

I will wager any amount of money you care to name that more than 99%  
of the document's readers (as it stands) will assume HTML4.

> and I'm sure Ben Adida of CC can speak up here.
>> However, it appears that they adopted this practice from RDFa;
>>   http://www.w3.org/TR/rdfa-syntax/#relValues
>> which, in turn, *does* rely upon XHTML. However, XHTML does *not*
>> specify the @rel value as a QName (or CURIE, as RDFa assumes);
>> http://www.w3.org/TR/2008/REC-xhtml-modularization-20081008/abstraction.html#dt_LinkTypes
>> "Note that in a future version of this specification, the Working
>> Group expects to evolve this type from a simple name to a Qualified
>> Name (QName)."
>> So, that's an expectation, not a current specification.
> In fact it is a current specification. RDFa specifies a version of  
> XHTML that defines the meaning of CURIEs in rel and rev values. Note  
> that this is also not invalid HTML4 (which also allows such values  
> in a rel - they are CDATA - but doesn't specify what they mean).

refers to
which contains
which refers to, for the Hypertext module (note 'latest version' URI):
which leads back to
i.e., the same, albeit most recent (instead of versioned) URI for

Even taking the other road and going with the contemporary version,
it's still just short names, with no reference to CURIEs or QNames at  

What am I missing?

The only place I see this defined is in the RDFa syntax document  
itself -- do you mean that is the specification of authority? I note  
that it specifies /html/@version="XHTML+RDFa 1.0", and it has its own  
DTD, so in a way I suppose it's not really an extension to XHTML, but  
a re-definition of it...

>> Of course, this conflicts with the Link draft;
>>  http://tools.ietf.org/id/draft-nottingham-http-link-header-04.txt
>> which we've worked pretty hard to come to consensus on across a broad
>> selection of communities (Atom, POWDER, OAuth, HTTP, and
>> optimistically, HTML5).
>> A few observations and questions;
>> 1) I'm more than happy to specify in the Link that in XHTML, a link
>> rel value is indeed a QName, if XHTML chooses to take that position
>> (although I believe a URI is a better fit than a QName here, as in
>> most other places). Can we get a current reading from the XHTML world
>> on this?
> A CURIE is a URI not a QName, so you're OK.

I haven't paid a lot of attention to them to date, but as far as I can  
see, a CURIE is most definitely not a URI; at most, it's a shorthand  
for one.

> CCing the XHTML2 WG and/or RDFa group would have helped in this case  
> if you wanted a response from them :-)

I wanted to get a feel from an architectural standpoint before talking  
to WGs about potentially irrelevant problems, but point taken.

>> 2) However, it seems like RDFa is jumping the gun by assuming @rel is
>> a CURIE right now.
> See above. It is already a Rec.
> [All the rest snipped since it was based on the assumption that XHTML 
> +RDFa isn't a Rec].

As I said before, the third point is IME the most concerning. Having  
two subtly incompatible syntax for the same attribute in HTML and  
XHTML isn't a great situation, but assuming that one is valid to use  
in the other is far more troublesome.


Mark Nottingham     http://www.mnot.net/
Received on Friday, 27 February 2009 10:55:12 UTC

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