Structurally it's a renamed ZIP file containing a pre-defined collection of XHTML, XML, NCX, OPF, and HTML/CSS content files. So it's not quite just HTML/CSS w

Structurally it's a renamed ZIP file containing a pre-defined collection of XHTML, XML, NCX, OPF, and HTML/CSS content files. So it's not quite just HTML/CSS when packaged up, but it is just HTML/CSS when it comes to the actual text content. Other than getting the various constituent files zipped up, with their interrelated contents synced, the only other oddity is that the renamed ZIP must always start with an uncompressed 'mimetype' file. The IDPF maintain the standard. The easy one is v2 (http://idpf.org/epub/201 http://idpf.org/epub/201) but that is now deprecated. Unfortunately v3 allows more interactivity and scripting - and we all know how bad the tech industry is at keeping that kind of stuff secure.