Summary of current state of ISSUE-135

The aim of ISSUE-135 is to prevent a non-RDFa @rel to disable the new
behavior of @property in RDFa+HTML5. In HTML5, @rel is used for many
purposes ([1] and [2]), many of them are irrelevant to RDFa. When HTML
authors use these values in @rel, they most likely don't do it with RDFa in
mind, and in this context the behavior of @property should not change when
a non-RDFa @rel is added to the same element.

In other words, the following two paragraphs should generate the same
triples:
<p vocab="http://schema.org/" typeof="Person">
   My name is <a href="http://example.com/" property="homepage">Stephane
Corlosquet</a>.
</p>
<p vocab="http://schema.org/" typeof="Person">
   My name is <a href="http://example.com/" property="homepage"
rel="me">Stephane Corlosquet</a>.
</p>

This issue has been discussed on the mailing list [3] and then during the
call on May 10th [4]. The following two options were discussed on the call:
1) If you have an element that has both @rel and @property in HTML5, then
the @rel can only take CURIEs, which will result in things like
rel="nofollow" being ignored
2) There is a more global one that in HTML5+RDFa a @rel value can only have
CURIEs.

The following resolution was taken (essentially option 1):
"If @property and @rel/@rev are on the same elements, the non-CURIE and
non-URI @rel/@rev values are ignored. If, after this, the value of
@rel/@rev becomes empty, then the then the processor must act as if the
attribute is not present."

This resolution ensures that rel="license" on an element with no @property
is still supported.

Here is a quick survey of some authoritative sites which are using or
promoting rel="license". I found that very few are combining @property with
@rel in the same element, and when they do, they always use cc:license in
@rel. In other words, I could not find any example that would break with
the option choosen above. Here are the sources I looked at:

# No use of @property and @rel in the same element:
A random wikipedia page:
http://en.wikipedia.org/wiki/The_Garden_of_Forking_Paths
A random Flickr page: http://www.flickr.com/photos/60223652@N00/2677272571/
http://microformats.org/wiki/rel-license
http://www.alistapart.com/articles/introduction-to-rdfa/
http://reference.sitepoint.com/html/rel-mf

# Use of @property and @rel in the same element using CURIEs:
http://wiki.creativecommons.org/RDFa
http://labs.creativecommons.org/2011/ccrel-guide/
http://labs.creativecommons.org/2011/ccrel-guide/examples/multiple_textimage.html
http://wiki.creativecommons.org/License_Deeds_%28Metadata%29

# Use of @property and rel="license":
*none*

Steph.

[1] http://www.w3.org/TR/html5-author/links.html#linkTypes
[2] http://microformats.org/wiki/existing-rel-values
[3] http://www.w3.org/2010/02/rdfa/track/issues/135
[4]
http://www.w3.org/2010/02/rdfa/meetings/2012-05-10#ISSUE__2d_135__3a__RDFa_Lite_and_non__2d_RDFa___40_rel_values