I tried converting a book with '&' in the title. It generates 3 FATAL errors with epub check. These need to be replaced by '&'.
After I made these edits, there were still a couple of errors (AZW3 contains a fixed-layout format) but these don't seem to create issues, at least for Apple Books:
Code:
ERROR(HTM-046): Signs and Symbols_ An Illustrated Guide to - Dk.epub/OEBPS/Text/cover_page.xhtml(8,8): Fixed layout document has no "viewport" meta element.
ERROR(OPF-014): Signs and Symbols_ An Illustrated Guide to - Dk.epub/OEBPS/Text/cover_page.xhtml(-1,-1): The property "svg" should be declared in the OPF file.
By the way, thanks for this plugin.
Calibre is unable to convert this format to epub. Comic book/manga (made from series of image files) convert okay, it is those that start life as PDF that appear to be problematic.
Kovid does not claim calibre supports conversion to FXL epub (I think he has said 'does NOT support'), but it would be nice to have. I would do a PR if I had more confidence that I could figure it out, and didn't have more immediate demands on my time.