I just search for occurrences of each class name in the xhtml and delete it if the search comes up empty. Yeah, it can be a bit time consuming, but in general, cleaning up the code in a book is almost
always time consuming anyway, but at least you only have to do it once (for each book).
\bsuspected-unused-classname\b
A plugin API will be so welcome when it happens.
(that's just wishful thinking not a nudge or anything
)