According to Success Criterion 2.4.8 (Location), link elements can be used to denote programmatically-determined relations between documents.
This example will emit an error about the lack of a "rel" attribute. Instead, it has a "rev" attribute, which used to indicate a reverse link - often, to the author using the relation code "made". Reverse links are for all intents and purposes obsolete (and is so in HTML5 - rev="made" is now rel="author"), so is not recognised.