rel=”tag” is specifically designed for “tagging” content, typically web pages (or portions thereof, like blog posts).
rel=”tag” is NOT designed for “tagging” arbitrary URLs or external content. There is demand for a general decentralized syntax for tagging URLs external to the current page, but this is not meant for that. See xFolk and hReview for ways to tag arbitrary URLs.
http://microformats.org/wiki/rel-tag
Example of the rel-tag
<a rel="tag" href="/tag/wordpress">WordPress</a>
Note it is the end part of url of the link that it points to rather than the word between the a tags.
