Error message generated for valid ISO8601 date [BUG] Checking for unused files which are not in the manifest [ENHANCEMENT] Existence of files referenced in guide not checked [BUG] Version r128 has broken test suite [BUG]Download epubcheck 1.1-rc1: epubcheck-1.1-rc1.jar. Note that you will need to know how to run the command-line epubcheck for this, and is intended for developers only. Please report issues to the epubcheck issues list.
Now that it's being worked on again, we now have 2 ways to verify an Epub: Flight Crew and EpubCheck. I'm going to let pros decide on which tool they should use, but I think the average user would be better off using Flight Crew. It's easier to install and run and it gives you better error messages. EpubCheck requires that you have some programming experience in order to use it. At the very least you need to know about the command line in Windows.