EPUB3

EPUB 3 is an open e-book standard designed for digital publications that can be read on a variety of devices. It is built on web technologies such as HTML5, CSS, and SVG, and represents the third major version of the EPUB format. The standard was originally developed by the International Digital Publishing Forum (IDPF) and, after the IDPF merged with the World Wide Web Consortium (W3C) in 2017, EPUB 3 has been maintained under W3C stewardship.

EPUB uses the Open Container Format (OCF), a ZIP-based package that contains a mandatory mimetype file and a package document (content.opf) describing metadata, the manifest of resources, and the spine that defines reading order. The package may also include a navigation document or a nav element to provide a table of contents. Content documents are typically XHTML, accompanied by CSS styles and, optionally, multimedia assets, fonts, and images. EPUB 3 supports both reflowable content and fixed-layout formats, making it suitable for text-heavy novels as well as image-rich layouts such as picture books.

Key features include support for HTML5, CSS3, and SVG, as well as optional SMIL-based media overlays for synchronized text and audio. The standard emphasizes accessibility through semantic markup and structural elements. DRM is not defined by EPUB itself; publishers may apply proprietary restrictions through distributors.

EPUB 3 is widely supported by modern e-readers and apps, including Apple Books, Google Play Books, Kobo, and Readium-based software, though some older devices may offer limited or no support for EPUB 3 features.