By the way, I can recall a
discussion on mobileread regarding EPUB validation tests.
When someone creates eBooks for personal use, it might be irrelevant whether his/her EPUBs pass the EPUB validation check if his/her eReader can display them correctly. But having a "valid" EPUB is important to publishers and writers.
Here is a link to a discussion thread on LinkedIn posted by a crime novelist
David (Alexander) Grace, a new fan of Atlantis Word Processor, I think.