@neko @meso @snacks amazon is using the mobipocket format which is ultimately derived from some record format you had to use on PalmOS. sometimes. there's like seven variations of a kindle file now, some of which are still mobis and some are abominations of shit taped on top of epub/mobi with special drm wrappers.

epub is idk. i've made version 2 and 3 files from time to time. its mostly an xml manifest or two and then the xhtml pages. as long as you break up the chapters in to separate files its fine. there's some dinguses that do not, and cram the whole 700 page book in one xhtml, which *does* make a ten year old kobo reader chug a bit, but its easy to not fuck this up.