Off the top of my head, I would probably throw the thing at HTML::Parser, and check for any tag that doesn't match your list of acceptable tags. Any bad tags would prompt an error and refusal to accept.

It does, like any other detainting procedure, need to use a list of acceptable tags, rather than a list of unacceptable tags. It's much easier to add to a list of acceptable tags ("Hey, my favourite tag, dl, isn't working! Add it!") than to maintain a list of unacceptable tags ("Darn, look what this idiot just did!").

Option 2: grab the source to Everything, and steal it. ;-)