Unused / missing class notification on epub validation

```
This mainly comes up when editing retail ebooks that I've purchased and want to
tweak but they often have tons of unused classes in their css. It's like they
have some giant css template with a class to cover every possible need. I like
to clean these up but it's a pain to have to keep going back and forth between
the css and the ebook to search for every single class to see if it's used.

It would be nice if, when performing an epub validation, it would tell you all
of the unused classes that exist in the css. Also, in case you refer to a class
in the ebook but forget to set the class up in the css or maybe delete one by
mistake, it would be nice if it notified you of any class references in the
ebook that don't exist in the css.
```

Original issue reported on code.google.com by `mbf62...@gmail.com` on 29 Jun 2011 at 9:27

Start by locating the EPUB validation entry point and the code that reads CSS class definitions and ebook class references. The issue provides no file or test names, so trace those paths first; done means validation reports both unused CSS classes and ebook-referenced classes missing from the CSS.

Written by the indexing model from the issue text.