When I was working on XFN - The XHTML Friends Network (effectively the first microformat), I specifically designed the underlying technology of XHTML Meta Data Profiles (XMDP) to *enable* all HTML rel/class additions/extensions (what would later become known as "microformats") to be *optionally* bound by URLs. And not just any URLs, but URLs that were compatible with and looked like RDF vocabulary URLs that ended with a "#" and term name. This was a deliberate design decision on my part, because I knew that there would be those who preferred to define their terms with URLs. Here is an HTML markup fragment that demonstrates this with the above-mentioned hCard 1.0:
<html><head profile="http://microformats.org/profile/hcard"> <title>a document with hCards</title></head> <p class="vcard"><span class="fn">Jeni Tennison</span> wrote an article, <cite><a href="http://www.jenitennison.com/blog/node/124">HTML5/RDFa Arguments</a></cite>, that compares and critically analyzes HTML5 and RDF approaches to representing and publishing data. </p> </html>
The terms "vcard" and "fn" which are used as class names are defined by the hCard XMDP and the respective URLs for those terms are created by referencing the fragment IDs in that document:
Thus providing the necessary URLs for any (meta)data system that stores/reasons about data based on vocabulary based on URLs (whether RDF or some other URL-based vocabulary store).
In practice, few people use XMDP profiles, well, except for at least the millions Wordpress blogs out there - just view source on them and you'll find:
profile="http://gmpg.org/xfn/11" near the top of the page.
The point is that those that want to use profiles have the *option* of using them, while not burdening everyone else with doing so.
Tantek 18:07, 22 August 2009 (UTC)