The original XFN specification is incomplete (as far as i think). Since my proposals and recommendations are ignored there i post them here.
The rel attribute adds a meaning to a link. It adds, what kind of link this is, or,
what is the relation of the target document for this dokument. Maybe you know
a href="anywhere.html" rel="next"blah...
This says, thet the relation of the target document is, that it is the next
document related to this document. The usage for personal relations is
very similar, for example when linking to a persons homepage.
This is very similar to the rel attribute, but reverse. To show an example:
a href="anywhere.html" rel="next" rev="prev"blah...
Exactly as in the example above the rel attribute shows the relation of the target document to this document. The rev attribute then shows, what this document is for the target document. Since the target document is the next document, this document is the previous document for the target document. This type of relationship is applicable to persons, too. The usage of this attribute was forgotten at XFN.
The same vocabulary is applicable to the class attribute. A simple example may show this:
We have a film on tv with
span class="person"Donald Duck
/span this evening.
address class="vcard me"
span class="fn"Siegfried Gipp
span class="street-address"Grundstr. 66
This specifies this address record not only as an address record with hCard markup, but it specifies this address record as my address record. This too was forgotten at XFN.