Comment by Javalicious

Wow. This brings up some (bad) memories of working with an .epub export about 10 years ago. We had some embedded fonts to work around some poor rendering in some of the readers we tested, but some of the readers ignored the fonts altogether, causing the content to render boxes (bangs head on table)

It looks like not a whole lot has changed in that space -- the readers are still the gate for what you can do with the format. Who's available to make a CanIUse for epub readers, to shame them into compliance? (only partly /s)