From the Microformats Wiki:
It is ACCEPTED that each microformat should have a profile URI, like the XFN profile.
Including a profile URI in your HTML like this:
<html>
<head profile="http://purl.org/uF/hCard/1.0/">
...… allows you to indicate that when you use mark-up like
class="fn" you’re definitely using that class in the hCard
sense, to indicate a formatted name. At the moment, very few microformat
tools pay attention to the document profile, but hopefully in the future, as
the microformat namespace becomes more crowded, more will.
A profile document is not:
There may exist some profile URIs which also fulfil one or more of the above roles. These profiles do not aim to.
The following profile URIs exist.
† = GRDDL-enabled.
¶ = non-XMDP profile.
The example given above shows how to link to a single profile using HTML 4 or XHTML 1.x. If you wish to use several profiles in a single document, you may separate them by white space:
<html>
<head profile="http://purl.org/uF/hCard/1.0/ http://gmpg.org/xfn/11">
...When multiple profiles are provided, their order is considered significant. If a term is defined in more than one profile, the first is considered definitive.
In XHTML 2 and HTML 5, the profile attribute is no longer allowed. An alternative syntax is defined for those versions of HTML:
<html>
<head>
<link rel="profile" href="http://purl.org/uF/hCard/1.0/" />
<link rel="profile" href="http://gmpg.org/xfn/11" />
...Although the need for profile URIs was recognised by the Microformats community almost three years ago, very little action has been taken on it, so I've decided to press forward with it myself. For most Microformats there were already sample XMDP profiles provided, but without stable URIs, and only as source code.
purl.org is a website dedicated to providing stable URIs. It is commonly used to provide URIs for profiles and namespace documents, being used for RSS 1.0, Dublin Core and eRDF amongst others.
And so I've matched up the community-provided profiles with purl.org to achieve the profiles above. Explanatory text has been added to each profile, showing authors how to use them, and they've been nicely styled.
In accordance with the spirit of the microformats community, these profiles and this accompanying explanatory document are released into the public domain.
You may re-use and abuse these documents as you wish, but you should take note that they are most valuable if they remain solely at the canonical URIs described within, and not as scattered copies all over the Internet with different URIs.