Sometimes when exporting a book to EPUB, the 'EPUB export warning(s)' dialog pops up.

The most obvious action for the user is to examine his documents to figure out what went wrong.

But that dialog box is modal. The user must close it before proceeding.

Sure, it would be nice to make that dialog box non-modal, so that the user could look at their documents while having the problem descriptions available.

Lacking that feature, though, you could make it easy to copy the problem text to another app (such as Windows Notepad). You allow the first step: Letting the user select the text. But you don't allow the second step: Letting the user copy the text to the clipboard using ^C.