Newer tags and html 5 is the same reason that I'm being forced to switch from GoLive (which I love) to Dreamweaver (which I loath).
Spent a better part of a day cleaning up the code from GoLive to Dreamweaver on
this site and it's only a dozen pages. It probably would have been easier and resulted in better code to have just started from scratch instead of trying to use the old code.