Brian Suda has a good, practical article on XFN on opera.dev — XFN encoding, extraction, and visualizations.

“In this article I will take a good look at XFN – the microformat for describing relationships between people. I will look briefly at what it is and the basic markup needed to add the information to your sites, before then going into depth, looking at the benefits you can get from that data by extracting it and using it in different ways.”

He covers the how and why of XFN and has good examples and code fragments. FOAF is only mentioned once in passing, however..

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