@BlinkRape @neko @waifu important issue with an ebook is the reader tends to need to seek, which is something ZIP excels at (because files are packed individually) whereas XAR, RAR, and 7Z are crapshoots, because the better compression comes from "solid" mode which basically turns the whole archive in to a single compressed tarball, which means you can no longer seek as the entire file has to be unpacked to read any point of it.

i think zstd has some seekable or rsync format mode that cuts it up in to blocks but i don't remember specifics