Like the REL attribute, REV is used to give the relationship(s) described by the hypertext link - consequently REV cannot be used unless an HREF is present. REV is semantically reversed compared with REL. I.E: A link from A to B with REL="X" means the same thing as a link from B to A with REV="X"
The value for REV is a comma-separated list of relationship values. For example
<A HREF="http://foo.edu/fe.html" REV="Usindex">sdfsddf</a>Values for the relationships and their semantics are registered by the HTML registration authority. The default relationship is none. For more information see the CERN HTML Documentation -- the relationships and their uses are described in the in the CERN documentation refered to in the bibliography.