.EPUB

Electronic Publication

Introduction

EPUB is the open standard for ebooks. It was developed by the International Digital Publishing Forum, which merged into the W3C in 2017; EPUB 3.3 became a W3C Recommendation in 2023. An EPUB is essentially a small website in a ZIP file: the chapters are XHTML pages styled with CSS, with images, fonts and a table of contents, so the text reflows to fit any screen.

Software

Structure

The ZIP archive must start with an uncompressed file named mimetype whose only content is application/epub+zip, so the type can be read from fixed bytes at the start of the file. META-INF/container.xml points to the package document, an .opf file that holds the book’s metadata, a manifest of every file and the spine, which sets the reading order. EPUB 3 books have a navigation document in XHTML; EPUB 2 books use an NCX file instead.

  1. zipmimetype application/epub+zip, stored first and uncompressed20 bytes
  2. zipMETA-INF/container.xml where the package document isXML
  3. zippackage.opf metadata, manifest and spineXML
  4. zipnav.xhtml the table of contentsXHTML
  5. zipchapters, CSS, images, fonts the contentvaries
The main parts inside an EPUB 3 container.