freejung - 10:24 pm on Jun 17, 2011 (gmt 0)

True, but on the other hand I would think you would have to have some pretty specialized requirements in order to need this at all. I don't recall ever having had duplicate content problems with non-HTML doctypes. The vast majority of webmasters would probably never even notice if they had a problem that this might be a solution to, let alone attempt to implement it.