ISO/IEC 23736-1:2020

INTERNATIONAL ISO/IEC
STANDARD 23736-1
First edition
2020-02
Information technology — Digital
publishing — EPUB 3.0.1 —
Part 1:
Overview
Technologies de l'information — Publications numériques — EPUB
3.0.1 —
Partie 1: Aperçu général
Reference number
©
ISO/IEC 2020
© ISO/IEC 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO/IEC 2020 – All rights reserved

Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are
members of ISO or IEC participate in the development of International Standards through technical
committees established by the respective organization to deal with particular fields of technical activity.
ISO and IEC technical committees collaborate in fields of mutual interest. Other international
organizations, governmental and non‐governmental, in liaison with ISO and IEC, also take part in the
work.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of document should be noted (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights.
Details of any patent rights identified during the development of the document will be in the
Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents) or the IEC
list of patent declarations received (see http://patents.iec.ch).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the World
Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT),
see www.iso.org/iso/foreword.html.
This document was prepared by the World Wide Web Consortium (W3C) (as EPUB 3 Overview) and
drafted in accordance with its editorial rules. It was adopted, under the JTC 1 PAS procedure, by Joint
Technical Committee ISO/IEC JTC 1, Information technology.
A list of all parts in the ISO/IEC 23736 series can be found on the ISO websitte.e
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
© ISO/IEC 2020 – All rights reserved iii

EPUB 3 Overview
Recommended Specification 26 June 2014
THIS VERSION
http://www.idpf.org/epub/301/spec/epub-overview-20140626.html
LATEST VERSION
http://www.idpf.org/epub3/latest/overview
PREVIOUS VERSION
http://www.idpf.org/epub/301/spec/epub-overview-20140228.html
A diff of changes from the previous version is also available.
All rights reserved. This work is protected under Title 17 of the United States Code. Reproduction and
dissemination of this work with changes is prohibited except with the written permission of the International
Digital Publishing Forum (IDPF).
EPUB is a registered trademark of the International Digital Publishing Forum.
Editors
Garth Conboy, Google Inc.
Matt Garrish, Invited Expert
Markus Gylling, International Digital Publishing Forum (IDPF)
William McCoy, International Digital Publishing Forum (IDPF)
MURATA Makoto, JEPA EPUB Study Group
Daniel Weck, DAISY Consortium
This document is informative
TABLE OF CONTENTS
1. Introduction
1.1. Overview
1.2. Roadmap
2. Features
2.1. Package Document
2.2. Navigation
2.2.1. Reading Order
2.2.2. Navigation Document
2.3. Linking
2.4. Metadata
2.5. Content Documents
© ISO/IEC 2020 – All rights reserved 1

2.6. Fixed Layouts
2.7. Rendering and CSS
2.8. Multimedia
2.9. Fonts
2.10. Scripting
2.11. Text-to-speech
2.12. Container
3. Global Language Support
3.1. Metadata
3.2. Content Documents
3.3. CSS
3.4. Fonts
3.5. Text-to-speech
3.6. Container
4. Accessibility
4.1. Navigation
4.2. Semantic Markup
4.3. Dynamic Layouts
4.4. Content Descriptions
4.5. Aural Renditions and Media Overlays
4.6. Fallbacks
4.7. Scripting
A. Glossary
B. Acknowledgements and Contributors
B.1. EPUB 3.0
B.2. EPUB 2.0.1
B.3. EPUB 1.0
References
› 1 Introduction
› 1.1 Overview
The EPUB® specification is a distribution and interchange format standard for digital publications and
documents. EPUB defines a means of representing, packaging and encoding structured and
semantically enhanced Web content — including HTML5, CSS, SVG and other resources — for
distribution in a single-file format.
EPUB 3, the third major release of the standard, consists of a set of four specifications, each defining
an important component of an overall EPUB Publication:
EPUB Publications 3.0.1 [Publications301], which defines the semantics and overarching
conformance requirements for each Rendition of an EPUB Publication.
EPUB Content Documents 3.0.1 [ContentDocs301], which defines profiles of XHTML, SVG and
CSS for use in the context of EPUB Publications.
EPUB Open Container Format (OCF) 3.0.1 [OCF301], which defines a file format and
processing model for encapsulating a set of related resources into a single-file (ZIP) EPUB
Container.
EPUB Media Overlays 3.0.1 [MediaOverlays301], which defines a format and a processing
model for synchronization of text and audio.
2 © ISO/IEC 2020 – All rights reserved

EPUB has been widely adopted as the format for digital books (eBooks), and these new
specifications significantly increase the format's capabilities in order to better support a wider range of
publication requirements, including complex layouts, rich media and interactivity, and global
typography features. The expectation is that EPUB 3 will be utilized for a broad range of content,
including books, magazines and educational, professional and scientific publications.
This document provides a starting point for content authors and software developers wishing to
understand these specifications. It consists entirely of informative overview material, including a
roadmap to the four building-block specification documents that compose EPUB 3.
Another informative document, EPUB 3 Changes from EPUB 2.0.1 [EPUB3Changes], describes
changes in EPUB 3 from the previous version, but is intended primarily for Authors and EPUB
Reading System vendors migrating from EPUB 2.0.1 to EPUB 3 and for those who anticipate
supporting both versions.
› 1.2 Roadmap
This section provides an overview of the EPUB 3 specifications by explaining in brief the components
of an EPUB Publication. Links to additional information within this document and to the specifications
are included.
An EPUB Publication, at its most basic level, is a bundled collection of resources that can be reliably
and predictably ingested by an EPUB Reading System in order to render its contents to a User. Each
EPUB Publication consists of one or renderings of its content, called Renditions.
Some of the resources in the EPUB Container facilitate the discovery and processing of the
Renditions, while others make up the content of the source publication. The latter, EPUB Content
Documents, are described in Content Documents and are fully defined in [ContentDocs301].
An EPUB Publication's resources are typically bundled for distribution as a ZIP-based archive with the
file extension .epub. As conformant ZIP archives, EPUB Publications can be unzipped by many
software programs, simplifying both their production and consumption. The container format is
introduced in Container and defined in [OCF301].
The container format not only provides a means of determining that the zipped content represents an
EPUB Publication (the mimetype file), but also provides a universally-named directory of informative
resources (/META-INF). Key among these is the container.xml file, which directs Reading Systems to
the root files of the available Renditions of the EPUB Publication (their Package Documents).
The Package Document is itself a kind of centralized information source for a given Rendition, storing
metadata about the specific work expressed by the Rendition, providing an exhaustive list of
resources and defining a default reading order. The Package Document is introduced in Package
Document and defined in [Publications301].
The preceding components of an EPUB Publication are not new to EPUB 3, and will be familiar to
anyone who has worked with EPUB Publications before, although they have been changed and
enhanced in this version. A new core addition to EPUB 3, however, is the Media Overlay Document,
which defines a means of synchronizing text and audio playback for a given Rendition. The Overlay
Document is introduced in Multimedia and defined in [MediaOverlays301].
The following example shows the resources a minimal single-Rendition "Hello World" EPUB
Publication might contain:
mimetype
META-INF/container.xml
© ISO/IEC 2020 – All rights reserved 3

Content/HelloWorld.opf
Content/HelloWorld.xhtml
While conceptually simple, an EPUB Publication is more than just a collection of HTML pages and
dependent assets in a ZIP package as represented in this example. The following sections of this
document delve into more detail about the primary features and functionality that EPUB Publications
provide to enhance the reading experience.
› 2 Features
This section covers the major features of EPUB, including important components and topics that
apply to the process of authoring EPUB Publications as a whole.
› 2.1 Package Document
Each Rendition of an EPUB Publication includes a single Package Document, which specifies all the
resources required to render that Rendition. The Package Document also defines a reading order for
linear consumption, and associates metadata and navigation information for the Rendition.
The Package Document represents a significant improvement on a typical Web site. A Web site, for
example, embeds references to its resources within its content, which, while a simple and flexible
means of identifying resources, makes it difficult to enumerate all the resources required to render it.
In addition, there is no standard way for a Web site to define that a sequence of pages make up a
larger publication, which is precisely what EPUB's spine [Publications301] element does (i.e., it
provides an external declarative means to explicitly specify navigation through a collection of
documents). Finally, the Package Document defines a standard way to represent metadata globally
applicable to a collection of pages.
The Package Document also includes a collection [Publications301] element, which allows
grouping of logically-related Publication Resources. This element exists to enable the development of
specialized content identification, processing and rendering features, such as the ability to define
embedded preview content, or assemble an index or dictionary from its constituent XHTML Content
Documents.
The Package Document and other Rendition-specific constructs are specified in [Publications301].
› 2.2 Navigation
› 2.2.1 Reading Order
A key concept of EPUB is that an EPUB Publication consists of multiple resources that can be
completely navigated and consumed by a person or program in some specific order.
Many types of publication have an obvious reading order, or logical progression through their content.
A novel is an example of a highly sequential document — it typically has a beginning, middle and end
— but not all publications are so ordered: a cookbook or collection of photographic images might be
considered to be more like a database. All documents do, however, have at least one logical ordering
4 © ISO/IEC 2020 – All rights reserved

of all their top-level content items, whether by date, topic, location or some other criteria (e.g., a
cookbook is typically ordered by type of recipe).
Each Rendition of an EPUB Publication defines at least one such logical ordering of all its top-level
content (the spine [Publications301] ), as well as a declarative table of contents (the EPUB Navigation
Document [ContentDocs301]). EPUB Publications make these data structures available in a machine-
readable way external to the content, simplifying their discovery and use.
EPUB Publications are not limited to the linear ordering of their contents, nor do they preclude linking
in arbitrary ways — just like the Web, EPUB Publications are built on hypertext — but the basic
consumption and navigation can be reliably accomplished in a way that is not true for a set of HTML
pages.
› 2.2.2 Navigation Document
Each Rendition of an EPUB Publication contains a special XHTML Content Document called the
EPUB Navigation Document, which uses the HTML5 nav element to define human- and machine-
readable navigation information.
The Navigation Document supersedes the NCX document [OPS2], and the inclusion of NCX
documents is only recommended for forward compatibility in older Reading Systems. The Navigation
Document, while maintaining the baseline accessibility and navigation support and features of the
NCX, introduces new functionality and rendering features to enhance navigation for all Users. Prime
among these are better support for internationalization (as an XHTML5 document itself, the
Navigation Document natively supports ruby annotations) and support for embedded grammars
(MathML and SVG can be included within navigation links).
As XHTML Content Documents, Navigation Documents also provide a flexible means of tailoring the
navigation display
...