Originally Posted by DiapDealer
You know me. I can't resist offering assistance to those who ask nicely for it.
Speaking of ever-helpful, the good folks at Apple have the kindness to "help" their customers by inserting a file, the iTunesMetadata.plist, which is embedded into the ePUB whenever a book is sideloaded to iBooks via iTunes. Now, here's the fun part: if you try to then upload a book to iBooks (iTunes Producer/Transport) with that file embedded in it, it will fail intake.
I actually have no bloody idea what this file does, but if I've had one client call me in a swivet because "the file [you] gave me is BAD and fails some kind of check," because they sideloaded it to iBooks first and then sent it on to Apple, I've had 50 or 100. This file has been an issue for the last few years--in fact, I first posted about it here on MR--but it's unrelated to the xml.options file needed for font embedding.