The exact meaning of a 'global identifier' (itemid)

I would like to know if the exact meaning of a Microdata global identifier
(itemid) has been documented?

I've been working on some test code to find out what can and cannot be
achieved by using @itemid and unfortunately I can't fully wrap my brain
around it since the different testing tools end up giving me different
results.

Now I've tried to look for info about @itemid on schema.org but can't find
anything. The only info out there I could find just says it should be
documented by the vocabulary itself.

sources:
http://www.w3.org/TR/microdata/#global-identifier
https://groups.google.com/forum/#!topic/schemaorg-discussion/YhF2cNGHVZ4
https://www.w3.org/Bugs/Public/show_bug.cgi?id=13007
http://lists.w3.org/Archives/Public/public-vocabs/2011Oct/0127.html

During my testing I got the impression the structured data linter is the
only tool that gets my markup right, but that's looking at it from an RDFa
perspective.

What is schema.org's perspective on this:

<body>
    <div itemid="CorporationPerson" itemscope itemtype="
http://schema.org/Corporation">
        <a itemprop="url" href="http://www.example.org">www.example.org</a>
    </div>

    <div itemid="Product" itemscope itemtype="http://schema.org/Product">
        <span itemprop="name">Donald Duck DVD</span>
        <link itemprop="brand" href="CorporationPerson" />
        <span itemprop="offers" itemscope itemtype="http://schema.org/Offer
">
            $<span itemprop="price">19.95</span>
            <meta itemprop="priceCurrency" content="USD">
        </span>
    </div>

    <div itemid="CorporationPerson" itemscope itemtype="
http://schema.org/Person">
        <span itemprop="name">Walt Disney</span>
    </div>
</body>

note: I'm not looking for @itemref solutions, extra <links> or different
order of HTML, those I can come up with myself just fine. I really just
want to know the workings of @itemid from a schema.org perspective.

Any thoughts?

-- 
*Jarno van Driel*
Technical & Semantic SEO Consultant
8 Digits - Digital Marketing Technologies

Tel: +31 652 847 608
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Received on Monday, 9 June 2014 18:24:39 UTC