EPUB 3

EPUB 3
Name	EPUB 3
Extension	.epub
Mime	application/epub+zip
Developer	International Digital Publishing Forum
Released	11 October 2011
Latest release version	3.3
Latest release date	25 May 2023
Genre	E-book
Extended from	EPUB 2.0.1
Standard	ISO/IEC TS 30135 (Parts 1-7)

EPUB 3 is the third major version of the EPUB standard, a widely adopted technical specification for digital publications and documents. Maintained by the W3C's Publishing@W3C group, it represents a significant evolution from its predecessor, EPUB 2.0.1, by deeply integrating modern web standards. The format is designed to create reflowable content that can adapt to different screen sizes and is now an official ISO technical specification.

Overview

EPUB 3 was formally approved by the International Digital Publishing Forum in October 2011, marking a pivotal shift towards using HTML5, CSS3, and ECMAScript as its core technologies. This alignment with open web standards allows publications to leverage the full feature set of modern web browsers and reading systems. The specification is developed as part of the W3C's Publishing@W3C activity, ensuring it remains interoperable with the broader Open Web Platform. A key milestone was the publication of EPUB 3.3 as a W3C Recommendation in May 2023, which also became ISO TS 30135.

Features

The format introduces extensive multimedia support, enabling native embedding of HTML5 video and audio elements without reliance on plugins. It provides comprehensive global language support through Unicode and includes vertical writing, Ruby annotation, and advanced font embedding for languages like Japanese, Arabic, and Hebrew. Enhanced styling and layout capabilities are achieved via CSS3, allowing for sophisticated typography and visual presentation. A major advancement is the inclusion of a dedicated JavaScript API for scripting interactive content, enabling complex educational tools, assessments, and immersive narratives.

Structure and Packaging

An EPUB 3 publication is fundamentally a ZIP-based archive that contains web content. Its spine is defined by the `package.opf` document, which lists all resources and the reading order. Each content document is an HTML5 file, styled with CSS and potentially enhanced with ECMAScript. The container is described by a `META-INF/container.xml` file, following the Open Container Format. All metadata, including that for Dublin Core terms, is expressed using the Package Document within the Open Packaging Format.

Accessibility

Accessibility is a foundational principle of EPUB 3, with features designed to meet guidelines like the W3C's Web Content Accessibility Guidelines. It mandates the use of semantic HTML5 elements to improve structure for assistive technologies such as screen readers. The standard supports synchronized pre-recorded media alternatives through SMIL and allows for extended descriptions. The EPUB Accessibility specification provides conformance requirements, and the format is widely used in initiatives like those by the DAISY Consortium and Bookshare to produce accessible educational materials.

Adoption and Support

Major platforms and devices have adopted EPUB 3, including reading software like Apple Books on iOS, Google Play Books on Android, and Adobe Digital Editions. E-reader devices from Kobo and certain Amazon Kindle models also provide support. The publishing industry, including academic publishers like the Oxford University Press and trade houses, utilizes it for complex textbooks and enhanced e-books. Government bodies, such as the United States Department of Defense, have mandated its use for digital delivery, and it is the preferred format for many library distribution services like OverDrive.

Comparison with Other Formats

Unlike the fixed-layout PDF, EPUB 3 is inherently reflowable, offering a better reading experience across devices. Compared to the proprietary Amazon Kindle format (AZW), EPUB 3 is an open standard developed by a consortium. While earlier versions like EPUB 2.0.1 lacked robust multimedia and scripting, EPUB 3 incorporates these as core features. It shares technological roots with formats like Apple's iBooks Author format but is vendor-neutral. Its reliance on HTML5 also creates a closer kinship with web publications than with traditional print-oriented digital formats.

Category:Electronic publishing Category:World Wide Web Consortium standards Category:Document file formats Category:Accessibility