> That's how ebooks already work right? Sort of, in the sense that any unzip tool will unpack an EPUB file (possibly after renaming it to a .zip extension rath

> That's how ebooks already work right? Sort of, in the sense that any unzip tool will unpack an EPUB file (possibly after renaming it to a .zip extension rather than .epub). However, it doesn't necessarily work the other way. You can't just zip the files at random and wind up with a valid EPUB, even if that exact same set of files was a valid EPUB before it was unzipped. The "mimetype" file in an EPUB zip is special. It has to be the very first entry in the archive. It also has to contain the string "application/epub+zip" (and nothing else) and must be stored uncompressed. A surprising number of zip tools make it hard to do this (e.g., by altering the file order as more files get added to the zip, or making it hard or impossible to store one file uncompressed while compressing the others). Most of the command line zip programs can do this with the proper command line flags, but zip libraries often make it a PITA. Source: have written EPUB generation software.