For our use we're only interested in a very small subset of XHTML. We use a rich text editor to let clients edit the contents of their web sites, and we don't want any tags included that could disrupt the design of the page. So only the most basic markup is allowed.
Should be easy to extend the script to take into account more of the elements specified in the HTML 5 draft, if anybody wants a more permissive purification...
Best of all, we just open-sourced the script.
Grab it from Github: http://github.com/biilmann/javascript-xhtml-purifier
Original anouncement (in Spanish): http://domestika.org/foros/956-kode/hilos/73209-depuracion_d...
As soon as you enable designmode on a document, every paste coming from something like Word will be transformed into delicious tag soup for you to deal with. No way to just disable that 'feature'.
What you don't see is the horrible HTML generated behind the scenes cough Sharepoint WYSIWYG editor cough.
It would work on half the browsers and need a dirty hack for the rest.