ISO/IEC 23761:2021

INTERNATIONAL ISO/IEC
STANDARD 23761
First edition
2021-02
Digital publishing — EPUB
accessibility — Conformance and
discoverability requirements for EPUB
publications
Edition numérique — EPUB Accessibilité — Exigences de conformité
et de découverte pour EPUB Publications
Member bodies are requested to consult relevant national interests in ISO/TC
46/SC 4,IEC/TC 100 before casting their ballot to the e-Balloting application.
PROOF/ÉPREUVE
Reference number
ISO/IEC 23761:2020(E)
©
ISO/IEC 2020

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COPYRIGHT PROTECTED DOCUMENT
© 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
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Published in Switzerland
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Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Success techniques . 1
5 Application to older versions . 1
6 Discoverability . 2
6.1 General . 2
6.2 Package metadata . 2
6.3 Linked metadata records . 3
7 Accessible publications . 3
7.1 General . 3
7.2 Relationship to WCAG . 3
7.3 WCAG conformance . 4
7.3.1 WCAG conformance requirements . 4
7.3.2 Evaluating WCAG conformance. 4
7.4 EPUB requirements. 5
7.4.1 Page navigation . 5
7.4.2 Media overlays playback . 6
7.5 Conformance reporting . 6
8 Optimized publications . 8
9 Distribution . 9
Annex A (informative) EPUB accessibility vocabulary .10
Bibliography .12
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ISO/IEC 23761:2020(E)

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. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (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 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 Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 34, Document description and processing languages.
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.
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Introduction
This document, EPUB accessibility, addresses two key needs in the EPUB® ecosystem:
— discoverability of the accessible qualities of EPUB publications;
— evaluation and certification of accessible EPUB publications.
The provision of accessibility metadata facilitates informed decisions about the usability of an EPUB
publication. Consumers can review the qualities of the content and decide whether an EPUB publication
is appropriate for their needs, regardless of whether it meets the bar of being certified broadly
accessible. At a minimum, all EPUB publications that conform to this document meet the accessibility
metadata requirements described in Clause 6.
Although it has always been possible to create EPUB publications with a high degree of accessibility, this
document also sets formal requirements for content to be certified as accessible. These requirements
provide authors a clear set of guidelines to evaluate their content against and allow certification of
quality. An accessible EPUB publication is one that meets the accessibility requirements as described in
Clause 7.
The document also establishes how to identify content that is optimized for specific user needs so
cannot meet broad accessibility requirements. The requirements for optimized publications are
described in Clause 8.
This document does not target a single version of EPUB. It is designed to be applicable to EPUB
[5]
publications that conform to any version or profile (e.g. EPUB 2 or ISO/IEC 23736-1), including future
versions of the standard.
Ideally, these guidelines will be instructive in evaluating any digital publication built on Open Web
technologies, although ensuring such application is outside the scope of this document.
NOTE For additional background on the decisions that went into this document, refer to EPUB Accessibility
[6]
Frequently Asked Questions .
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INTERNATIONAL STANDARD ISO/IEC 23761:2020(E)
Digital publishing — EPUB accessibility — Conformance
and discoverability requirements for EPUB publications
1 Scope
This document specifies content conformance requirements for verifying the accessibility of EPUB
publications. It also specifies accessibility metadata requirements for the discoverability of EPUB
publications.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 15836-2, Information and documentation — The Dublin Core metadata element set — Part 2: DCMI
Properties and classes
ISO/IEC 23736-2, Information technology — Digital publishing — EPUB 3.0.1 — Part 2: Publications
ISO/IEC 40500, Information technology — W3C Web Content Accessibility Guidelines (WCAG) 2.0
RFC 3987, Internationalized Resource Identifiers (IRIs). M Duerst, et al. January 2005. Available at
https:// tools .ietf .org/ html/ rfc3987
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/IEC 23736-2 and
ISO/IEC 40500 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Success techniques
This document takes an abstract approach to the accessibility requirements for EPUB publications,
similar to how WCAG 2.0 (ISO/IEC 40500) separates its accessibility guidelines from the techniques to
achieve them. This approach allows the guidelines to remain stable even as the format evolves.
[7]
To facilitate this approach, the companion EPUB Accessibility Techniques document outlines
conformance techniques. These techniques explain how to meet the requirements of this document for
different versions of EPUB.
5 Application to older versions
This document is designed to be applicable to any EPUB publication, even if the content conforms to
[5]
an older version of EPUB that does not refer to this document (e.g. EPUB 2 ).
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Authors of such EPUB publications are encouraged to create content in conformance with the
accessibility and discoverability requirements of this document. Upgrading to the latest version of
EPUB to get access to the most advanced accessibility features and techniques is also encouraged.
6 Discoverability
6.1 General
Unlike web pages, EPUB publications are designed to be distributed through many channels for personal
consumption — a model that has made EPUB a successful format for ebooks and other types of digital
publications. A consequence of this model, however, is that specific details about the accessibility of a
publication need to travel with it.
An online bookstore aggregating content from publishers and authors, for example, does not know
the production quality that went into each submission unless the publisher informs them through
metadata.
Ensuring that the accessible qualities of an EPUB publication can be discovered by any interested party
is therefore a primary concern. Users need to be able to gauge the usability of an EPUB publication when
they purchase, borrow or otherwise obtain it, a determination that requires knowing the affordances
made to meet the accessibility requirements.
Similarly, content that does not meet the accessibility requirements of this document does not
necessarily fail to meet the needs of individual users.
Only through the provision of rich metadata can a user decide if the content is suitable for them.
6.2 Package metadata
All EPUB publications shall include accessibility metadata in the package document that exposes their
accessible properties, regardless of whether the publications also meet the accessibility (Clause 7) or
optimization (Clause 8) requirements.
EPUB publications shall include the following accessibility metadata:
— Access modes — a human sensory perceptual system or cognitive faculty necessary to process or
perceive the content (e.g. textual, visual, auditory, tactile).
— Accessibility features — features and adaptations that contribute to the overall accessibility of the
content (e.g. alternative text, extended descriptions, captions).
— Accessibility hazards — any potential hazards that the content presents (e.g. flashing, motion
simulation, sound).
— Accessibility summary — a human-readable summary of the overall accessibility, which includes a
description of any known deficiencies (e.g. lack of extended descriptions, specific hazards).
EPUB publications should include the following accessibility metadata:
— Sufficient access modes — a set of one or more access modes sufficient to consume the content
without significant loss of information. An EPUB publication can have more than one set of sufficient
access modes for its consumption depending on the types of content it includes (i.e. unlike access
modes, this property takes into account any affordances for content that is not broadly accessible,
such as the inclusion of transcripts for audio content).
EPUB publications may include the following accessibility metadata:
— Accessibility application programming interfaces (APIs) — to indicate the resource is compatible
with the specified accessibility API. This property is typically only used to indicate that the use of
[3]
scripting in an EPUB publication follows Accessible Rich Internet Applications (WAI-ARIA) 1.1
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authoring practices, as compatibility with operating system accessibility APIs is a concern for
reading systems.
— Accessibility controls — input methods that can be used to access the content (e.g. keyboard, mouse).
Authors may include additional accessibility metadata not specified in this subclause.
[7]
NOTE See Discovery Metadata Techniques in EPUB Accessibility Techniques for more information on
these properties and how to include them in different versions of EPUB. See also DIST-002: Include accessibility
[7]
metadata in distribution records in EPUB Accessibility Techniques for more information on including
accessibility metadata in other formats.
6.3 Linked metadata records
Accessibility metadata can also be included in linked records (see ISO/IEC 23736-2) (i.e. metadata
records referenced from link elements), but the inclusion of such metadata solely in a linked record
does not satisfy the discoverability requirements of this document.
7 Accessible publications
7.1 General
EPUB is built on the Open Web Platform, with HTML, CSS, JavaScript and SVG, the core technologies
used for content authoring. The use of these technologies means that EPUB publications can be
authored with a high degree of accessibility simply through the proper application of established web
accessibility techniques.
The primary source for the production of accessible web content is the W3C Web Content Accessibility
Guidelines (WCAG) 2.0 (ISO/IEC 40500). This document leverages the extensive work done in WCAG 2.0
to establish benchmarks for accessible content, and the same four high-level content principles —
perceivable, operable, understandable and robust — are central to creating EPUB publications that are
accessible.
This clause defines how to apply the conformance criteria defined in WCAG 2.0 and addresses qualities
unique to EPUB publications.
EPUB publications authored to comply with the requirements in this clause will have a high degree of
accessibility for users with a wide variety of reading needs and preferences.
7.2 Relationship to WCAG
WCAG 2.0 (ISO/IEC 40500) and its associated techniques (WCAG 2.0 techniques) provide extensive
coverage of issues and solutions for web content accessibility — from tables to embedded multimedia
to rich semantics. They represent the foundation that this document builds upon.
This document does not repeat the requirements or techniques introduced in those documents,
as it risks breaking compatibility between the two standards (e.g. putting guidance out of sync, or
in conflict). At the same time, although the requirements are not individually called out, it does not
diminish their importance in creating EPUB publications that are accessible.
This document instead defines how to apply WCAG 2.0 to an EPUB publication — which is a collection
of web documents as opposed to a single page (7.3.2.1) — and adds an additional set of requirements
(7.4). These requirements are no more or less important than those covered in WCAG 2.0; they are
simply necessary to follow for EPUB publications. (The relationship to WCAG 2.0 is explained for each
requirement in its respective subclause.)
[7]
The same is true of the techniques in the EPUB Accessibility Techniques document. It provides
coverage of techniques that are unique to EPUB publications, or that need clarification in the context of
an EPUB publication. It does not mean that the rest of the WCAG techniques are not applicable.
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As a result, although this clause can be read without deep knowledge of WCAG 2.0 conformance, to
implement the accessibility requirements of this document will require an understanding of WCAG 2.0.
Because this document adds requirements that are not a part of WCAG 2.0, an EPUB publication can
conform to WCAG 2.0 without conforming to this document.
7.3 WCAG conformance
7.3.1 WCAG conformance requirements
EPUB publications shall meet WCAG 2.0 Level A (ISO/IEC 40500) to be conformant with this document,
but it is recommended that they meet Level AA.
NOTE Although this document only requires Level A conformance, local and national laws can influence the
level of conformance an EPUB publication has to meet to be considered accessible. Level AA conformance is often
cited as the benchmark for accessibility in legal frameworks and policies, for example. Additionally, any procurer
or distributor of EPUB publications can demand higher conformance requirements than the baseline defined here.
7.3.2 Evaluating WCAG conformance
7.3.2.1 Page and publication
The WCAG 2.0 principles focus on the evaluation of individual web pages, but an EPUB publication more
closely resembles what WCAG 2.0 ref
...