XHTML Friends Network is a simple piece of mark-up for identifying human relationships of links. Aimed at personal websites – weblogs and blogrolls in particular – you simply add a rel attribute to your link with a space-separated list of relationships, e.g.

<a href="http://www.adactio.com/"
   title="Jeremy Keith"
   rel="friend met colleague neighbor">

The possible values of relationship are pre-defined and in most cases are deliberately open to interpretation. For example, the two work-related values, colleague and co-worker do not necessarily imply each other. A co-worker is someone who works for the same company as you, whereas a colleague is someone who does the same job as you (a fellow doctor or Web designer).

XFN was only released last month so as yet there’s no direct application. That said XFN came from the minds of Tantek Çelik, Eric Meyer and Matthew Mullenweg, some of the cleverest minds in the business, so I foresee a bright future. If the major blogging and blogroll tools adopt XFN then there will be a gaping hole for a spidering tool to show all these relationships (maybe graphically with SVG – now that would be cool). For now we have a nifty bookmarklet developed by Ben Zanin which lists all XFN-enabled links in a page and CSS2 selectors to format given relationships. For instance, I display an asterisk next to blogs belonging to folks I’ve actually met:

a[rel~="met"]:after {content: " *";}

† The Burgled list of Web sites on the Clagnut home page is a blogroll – a list of blogs that I read regularly.