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+Ian Hickson, could you point me to the use case(s) that led you to introducing itemref in microdata? I've looked through the list of use cases at but none of them mention itemref (perhaps it was called something else at that point and I missed it). Many thanks in advance.
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The use case is microdata fragments that are split across parts of the page, for example if each column in a table is a different item. We tried various different ways of doing it, this one was the least problematic. I'm not a huge fan of the way this part of the microdata feature came out, but every time I try to remove it people beat me back from the keyboard. :-)
:) Thanks Ian. I know that itemref supports it, but did you have any strong use cases that were about two items sharing the same set of properties? Or was that just included because it was easier to allow it than not?

I'm trying to work out whether to push the RDFWAWG to support similar functionality in RDFa or not.
As far as I can recall, being able to use the same properties in two different items was just something that the design allowed as a side-effect, it wasn't the goal of the feature. IIRC, the first design was an itemfor="" attribute on the property itself (basically the same thing but with the link going the other way), which doesn't allow it. We moved away from this because it was confusing to authors, not because it didn't allow shared properties.

(Actually, shared properties result in some weird complications for validation.)
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