EPUB Accessibility 1.0

Conformance and Discovery Requirements for EPUB Publications

Proposed Specification 14 October 2016

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Matt Garrish, Invited Expert

George Kersher, DAISY Consortium

Charles Lapierre, Benetech

Avneesh Singh, DAISY Consortium


Romain Deltour, DAISY Consortium

Markus Gylling, International Digital Publishing Forum (IDPF)

Bernhard Heinser, Access for All

Jean Kaplansky, Invited Expert

Madeleine Rothberg, Invited Expert

Tzviya Siegman, John Wiley & Sons

Jason White, Invited Expert

Copyright © 2010-2016 International Digital Publishing Forum™

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.

  1 Overview

  1.1 Purpose and Scope

This section is informative

This specification, EPUB Accessibility, addresses two key needs in the EPUB® ecosystem:

  1. evaluation and certification of accessible EPUB Publications;

  2. discovery of the accessible qualities of EPUB Publications.

Although it has always been possible to create EPUB Publications with a high degree of accessibility, this specification sets formal requirements to meet to certify content as accessible. These requirements provide Authors a clear set of guidelines to evaluate their content against, and allow certification of quality.

The inclusion of accessibility metadata, on the other hand, 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.

This specification defines three categories of compliance for EPUB Publications:

This specification does not target a single version of EPUB. It is designed to be applicable to EPUB Publications that conform to any version or profile, 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 specification.


For additional background on the decisions that went into this specification, refer to the informative [Accessibility FAQ].

  1.2 Success Techniques

This specification takes an abstract approach to the accessibility requirements for EPUB Publications, similar to how [WCAG 2.0] separates its accessibility guidelines from the techniques to achieve them. This approach allows the guidelines to remain stable even as the format evolves.

To facilitate this approach, the companion [EPUB Accessibility Techniques] document outlines conformance techniques. The techniques explain how to meet the requirements of this specification for different versions of EPUB.

  1.3 Application to Older Specifications

This section is informative

This specification is designed to be applicable to any EPUB Publication, even if the content conforms to an older specification that does not make reference to this one (i.e., specifications prior to [EPUB 3.1]).

Authors of such EPUB Publications are encouraged to create content in conformance with the accessibility requirements of this specification, even though it is not normatively required.

  1.4 Terminology

Assistive Technology

This specification adopts the meaning of an assistive technology from [WCAG 2.0].

Note that an assistive technology is not always a separate application from a Reading System. Reading Systems often integrate features of standalone assistive technologies, such as text-to-speech playback.


The person(s) or organization responsible for the creation of an EPUB Publication. The Author is not necessarily the creator of the content.

EPUB Authoring Tool

This specification adapts the meaning of authoring tool from [ATAG 2.0]. An EPUB Authoring Tool differs only in that it is has to be able to create or modify an EPUB Publication.

EPUB Content Document

A document that conforms to one of the EPUB Content Document definitions.

EPUB Publication

A collection of one or more Renditions that represents a single intellectual or artistic work.


An EPUB Publication whose content is enhanced to be accessible by users with a specific need (e.g., dyslexia) or preferred reading modality (e.g., audio, tactile), so does not meet the broader accessibility requirements of [WCAG 2.0]. See Optimized Publications.

Package Document

The Package Document describes one Rendition of an EPUB Publication. It carries meta information, provides a manifest of resources and defines the default reading order.

Reading System

A system that processes EPUB Publications for presentation to a user.


A logical document entity that represents one rendering of an EPUB Publication.


Some terms have more precise meanings for a given version of EPUB. Refer to the appropriate specification for more information.

  1.5 Typographic Conventions

The following typographic conventions are used in this specification:


All markup (elements, attributes, properties), code (JavaScript, pseudo-code), machine-readable values (string, characters, media types) and file names are in red monospace font.

markup link

Links to markup and code definitions are in underlined red monospace font.


URIs are in navy blue monospace font.


Hyperlinks are underlined and blue.


Normative and informative references are enclosed in square brackets.


Terms defined in the Terminology are in capital case.

Term Link

Links to term definitions have a dotted blue underline.

Normative element, attribute and property definitions are in blue boxes.

Informative markup examples are in light gray boxes.


Informative notes are in green boxes with a "Note" header.


Informative cautionary notes are in red boxes with a "Caution" header.

  1.6 Conformance Statements

The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL in this document are to be interpreted as described in [RFC2119].

All sections and appendixes of this specification are normative except where identified by the informative status label "This section is informative". The application of informative status to sections and appendixes applies to all child content and subsections they contain.

All examples in this specification are informative.

  2 Conformance

  2.1 Discovery-Enabled EPUB Publications

The following requirements apply to a discovery-enabled EPUB Publication:

  2.2 Accessible EPUB Publications

An EPUB Publication must meet the following requirements to be accessible per this specification:

  2.3 Optimized EPUB Publications

An optimized EPUB Publication must meet the following requirements:

  3 Discovery

  3.1 Introduction

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. One downside to this model, however, is that specific details about the accessibility of a publication typically do not 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, so can only convey to consumers what is present in the 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 suitability of an EPUB Publication when they purchase, borrow or otherwise obtain it (e.g., will it be adequate for an educational setting). That the content meets the accessibility requirements of this specification is often not enough information; the specific affordances made to meet the requirements are equally important to know when determining usability.

Similarly, content that does not meet the requirements of this specification, while not broadly accessible, might still meet the needs of individual users. Only through the inclusion of rich metadata can a user decide if the content is suitable for them.

  3.2 Package Metadata

Every conformant EPUB Publication must include the following [schema.org] accessibility metadata:

  •   accessMode — the senses or faculties necessary to process or perceive the content (e.g., textual, visual, auditory, tactile).

  •   accessibilityFeature — features and adaptations that increase the overall accessibility of the content (e.g., alternative text, extended descriptions, captions).

  •   accessibilityHazard — any potential hazards that the content presents (e.g., flashing, motion simulation, sound).

  •   accessibilitySummary — a human-readable summary of the overall accessibility, which includes a description of any known deficiencies (e.g., lack of extended descriptions, specific hazards).

Inclusion of the following [schema.org] accessibility metadata is recommended:

  •   accessModeSufficient — a set of one or more access modes sufficient to consume the content without significant loss of information. An EPUB Publication might have more than one set of sufficient access modes for its consumption depending on the types of content it includes (i.e., unlike accessMode, this property takes into account any affordances for content that is not broadly accessible, such as the inclusion of transcripts for audio content).

Inclusion of the following [schema.org] metadata is optional:

  •   accessibilityAPI — indicates the resource is compatible with the specified accessibility API (typically only used to identify [WAI-ARIA 1.1] conformance).

  •   accessibilityControl — identifies input methods that can be used to access the content (e.g., keyboard, mouse).


See Discovery Metadata Techniques [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 metadata in distribution records [EPUB Accessibility Techniques] for more information on including accessibility metadata in other formats.


The above recommendations cover all [schema.org] accessibility properties at the time of publication. If new properties are added in the future, Authors are encouraged to include them, as applicable, until such time as this specification can be updated.

Inclusion of accessibility metadata from other vocabularies is optional.

  3.3 Linked Metadata Records

Accessibility metadata can also be included in linked records [Packages], but the inclusion of such metadata solely in a linked record does not satisfy the discovery requirements of this specification.

As the precedence given to linked records varies depending on the version of EPUB, Authors need to take care to ensure that accessibility metadata in the Package Document and any linked records do not contain contradictory statements, as it can affect the information a Reading System presents to the user.

  4 Accessible Publications

  4.1 Introduction

This section is informative

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 [WCAG 2.0]. This specification 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 accessible EPUB Publications.

This section defines how to apply the conformance criteria defined in [WCAG 2.0] and also addresses qualities unique to EPUB Publications.

EPUB Publications authored to comply with the requirements in this section will have a high degree of accessibility for users with a wide variety of reading needs and preferences.

  4.2 Relationship to WCAG

This section is informative

[WCAG 2.0] and [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 specification builds upon.

This specification 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 accessible EPUB Publications.

This specification instead adds an additional set of requirements for EPUB Publications. These requirements are no more or less important than those covered in WCAG; they are simply necessary to follow for EPUB Publications. (The relationship to WCAG is explained for each requirement in its respective section.)

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.

As a result, although this section can be read without deep knowledge of WCAG conformance, to implement the accessibility requirements of this specification will require an understanding of [WCAG 2.0].


Because this specification adds requirements that are not a part of WCAG, an EPUB Publication can conform to [WCAG 2.0] without conforming to this specification. An EPUB Publication that does not meet the requirements for EPUB Publications is not accessible to this specification, however.

The IDPF plans to work with W3C and the Web Accessibility Initiative to harmonize the requirements for EPUB Publications with WCAG.

  4.3 WCAG Conformance

  4.3.1 WCAG Conformance Requirements

EPUB Publications must meet [WCAG 2.0] Level A to be conformant with this specification, but it is recommended that they meet Level AA.

Note that local and national laws can influence the level of conformance an EPUB Publication has to meet to be considered accessible, as [WCAG 2.0] Level AA conformance is often cited as the benchmark for accessibility in legal frameworks and policies. In fact, any EPUB specification, and even vendor procurement requirements, can demand content that exceeds the minimum requirements of this specification.

Authors need to ensure they understand the requirements their content has to meet to be considered accessible in any jurisdiction or distribution context, including seeking any necessary legal advice. Minimum conformance with this specification does not supersede such requirements, and does not offer protection from any legal liability that might arise.

  4.3.2 Evaluating WCAG Conformance 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] refers to as a set of Web pages: "[a] collection of Web pages that share a common purpose".

Consequently, when evaluating the accessibility of an EPUB Publication, individual pages — or Content Documents, as they are known in EPUB nomenclature — cannot be reviewed in isolation. Rather, their overall accessibility as parts of a larger work also has to be evaluated.

For example, it is not sufficient for individual Content Documents to have a logical reading order if the publication presents them in the wrong order. Likewise, including a title for every Content Document is complementary to providing a title for the publication: the overall accessibility is affected if either is missing.

The [WCAG 2.0] guidelines for content to be perceivable, operable, understandable and robust therefore must be evaluated against the full EPUB Publication, not only to each Content Document within it.

More information about applying these guidelines to EPUB Publications is available in the [EPUB Accessibility Techniques]. Applying the Conformance Criteria

When evaluating an EPUB Publication, the [WCAG 2.0] Conformance Criteria are applied as follow:

  •   When determining compliance with a Conformance Level, the EPUB Publication as a whole must meet the conformance requirements of the level claimed.

  •   Authors must not use EPUB's fallback mechanisms to provide a conforming alternate version [WCAG 2.0], as there is no reliable way for users to access such fallbacks. If fallbacks are used, both the primary content and its fallback(s) must meet the requirements for the conformance level claimed. Examples of EPUB-specific fallback mechanisms include manifest fallbacks, bindings and content switching.

  •   When determining compliance with the "Full Pages" requirement (i.e., that parts of a page cannot be excluded when making a conformance claim), the entirety of each content document must achieve the conformance level and every content document in the publication must meet the stated conformance level.

  4.4 EPUB Requirements

  4.4.1 Page Navigation Objective

Provide navigation to static page break locations. Understanding this Objective

Statically paginated content is still ubiquitous, as print continues to be the most consumed medium for books both among the general reading public and in educational settings. Print is not the only source of static pagination, either: static page boundaries are also present in fixed-layout digital publications.

As a result, a non-visual reader in an environment where statically-paginated content is used is disadvantaged relative to his or her peers by not being able to easily locate the same locations in the publication (e.g., if a teacher instructs students to all turn to a specific page).

The inclusion of page boundary locations helps bridge this disparity by ensuring that those using reflowable media are not disadvantaged by their choice.

Providing page navigation also helps in reflowable publications that do not have a statically paginated equivalent. The default pagination of these publications by Reading Systems is not static, since it changes depending on the viewport size and user's font settings. As a result, coordinating locations among users of the same EPUB Publication can be complicated without static references. Meeting this Objective

Authors should include page navigation in an EPUB Publication whenever any of the following cases is true:

  •   the EPUB Publication is identified as the digital equivalent of a statically-paginated publication (e.g., included in a print/digital bundle).

  •   the EPUB Publication is offered as an alternative to a statically-paginated publication in an environment where the use of both versions can be reasonably predicted (e.g., education).

  •   the EPUB Publication and a statically-paginated publication are generated from a workflow that allows the retention of page break locations across formats.

Authors may include page navigation in reflowable EPUB Publications without statically paginated equivalents, but inclusion is not necessary to meet the requirements of this specification.

A conformant EPUB Publication must meet the following requirements when it includes page navigation:

  •   It must provide a means of locating the page break locations.

  •   It may include page break markers.

  •   It must identify the source of the page breaks.

In addition, if page numbers are read aloud in a synchronized text-audio playback of the content (e.g., EPUB 3 Media Overlays), Authors must identify the page numbers in the markup that controls the playback.

See Page Markers [EPUB Accessibility Techniques] for more information on the inclusion of page navigation in EPUB Publications. Relationship to WCAG

The inclusion of page navigation represents one method of achieving the [WCAG 2.0] Multiple Ways success criterion, as it provides another meaningful way for users to access the content (e.g., in addition to the table of contents, linear reading order and any other navigation aids).

Given the importance of page navigation in mixed print/digital environments, the requirement to include this feature has higher precedence than it would be given solely as one of many ways to meet the Multiple Ways success criterion.

  4.4.2 Media Overlays Playback Objective

Structure Media Overlays to provide more accessible playback experiences. Understanding this Objective

Media Overlays provide an accessible playback experience for anyone who benefits from having text and audio synchronized. They are also useful to users who only require audio playback, or only benefit from reading with text highlighting. Media Overlays also enable a seamless playback experience from beginning to end of an EPUB Publication for all these users.

The most basic Media Overlay Documents [Media Overlays] provide only minimal instructions to Reading Systems, however. They indicate the text to highlight and the audio clip that corresponds to the text. The result is that users only have basic start and stop options available.

Authors need to add structure and semantics to Media Overlay Documents to allow Reading Systems to present more usable experiences. With richer markup, a Reading System could provide the ability to skip past secondary content that interferes with the primary narrative, escape users from deeply nested structures like tables, and allow them to navigate through the sections of the publication without having to go to the table of contents. Meeting this Objective

Media Overlay Documents do not have to meet any additional requirements beyond those defined in [Media Overlays] to be conformant with this specification.

To improve the usability of Media Overlays, however, Authors are encouraged to ensure their EPUB Publications meet the following recommendations:


A future version of this specification might introduce stricter conformance requirements for Media Overlay Documents. Relationship to WCAG

The enhancements to Media Overlay Documents broadly fall under the objective of the [WCAG 2.0] Info and Relationships success criterion. Without structured and semantically meaningful playback sequences, the effect is to deprive users rich navigation of the content.

  4.5 Conformance Reporting

To indicate that an EPUB Publication conforms to the accessibility requirements of this specification, it must include a conformsTo property [DCTERMS] and an a11y:certifiedBy property [Accessibility Vocab].

The value of the conformsTo property must be one of the following IRIs:


The EPUB Publication meets all accessibility requirements and achieves [WCAG 2.0] Level A conformance.


The EPUB Publication meets all accessibility requirements and achieves [WCAG 2.0] [WCAG 2.0] Level AA conformance.


The EPUB Publication meets all accessibility requirements and achieves [WCAG 2.0] [WCAG 2.0] Level AAA conformance.

The a11y:certifiedBy property specifies the name of the party that certified the content. The certifier of the content could be the same party that created the EPUB Publication, but can also be a third party accessibility certifier.

The following example shows an EPUB 3 Publication that has been self-certified by the publisher (the values of the dc:publisher and a11y:certifiedBy property are the same).

  <dc:publisher>Acme Publishing Inc.</dc:publisher>
  <meta property="a11y:certifiedBy">Acme Publishing Inc.</meta>
  <link rel="dcterms:conformsTo" href="http://www.idpf.org/epub/a11y/accessibility-20161014.html#wcag-aa"/>

The following example shows an EPUB 3 Publication that has been certified by a third party (the values of the dc:publisher and a11y:certifiedBy property differ).

  <dc:publisher>Acme Publishing Inc.</dc:publisher>
  <meta property="a11y:certifiedBy">Foo's Accessibility Testing</meta>
  <link rel="dcterms:conformsTo" href="http://www.idpf.org/epub/a11y/accessibility-20161014.html#wcag-aa"/>

The following example shows an EPUB 3 Publication that has been self-certified by the author.

  <dc:creator>Jane Doe</dc:creator>
  <meta property="a11y:certifiedBy">Jane Doe</meta>
  <link rel="dcterms:conformsTo" href="http://www.idpf.org/epub/a11y/accessibility-20161014.html#wcag-aa"/>

The following example shows a self-certified EPUB 2 Publication.

  <dc:publisher>Acme Publishing Inc.</dc:publisher>
  <meta name="dcterms:conformsTo" content="http://www.idpf.org/epub/a11y/accessibility-20161014.html#wcag-aa"/>
  <meta name="a11y:certifiedBy" content="Acme Publishing Inc."/>


If an EPUB Publication is certified by an organization, users will typically want to know the name of that organization. Including the name of the individual(s) who carried out the assessment, instead of the name of the certifying organization, is generally discouraged, as it can diminish the trust the user has in the claim.

If the party that certifies the content has been issued a credential or badge that establishes their authority to certify content accessible, that information can be supplied in an a11y:certifierCredential property [Accessibility Vocab].

The following example shows a credential.

<meta property="a11y:certifierCredential">A+ Accessibility Rating</meta>

If the party that certifies the content has provided a detailed report of its assessment, a link to the assessment can be provided in an a11y:certifierReport property [Accessibility Vocab].

The following example shows a link to a remotely-hosted accessibility report.

<link rel="a11y:certifierReport"

The following example shows a link to a locally-hosted accessibility report.

<link rel="a11y:certifierReport" href="reports/a11y.xhtml"/>


As each metadata format is unique in what it can express, this specification does not mandate how conformance metadata is expressed outside of the Package Document.


This specification does not define a conformance level for EPUB Publications that only meet the discovery metadata requirements, as the usability of such content by any given user can only be determined from the accessibility metadata. Reporting requirements for Optimized Publications are defined in the next section.

  5 Optimized Publications

Although [WCAG 2.0] provides a general set of guidelines for making content broadly accessible, conformant content is not always optimal for specific user groups. Conversely, content optimized for a specific need or reading modality is often not conformant to [WCAG 2.0] because it is not designed for a broad audience. In these cases, failing to achieve a WCAG conformance level does not make the publications any less accessible to their intended audience.

To account for this discrepancy, this specification places importance on the inclusion of discovery metadata. An optimized EPUB Publication is discoverable to its intended audience through the inclusion of rich metadata, even if it is not identified as broadly accessible per this specification.

In addition to the metadata requirements defined in Discovery, an optimized EPUB Publication must identify the standard or guidelines the content adheres to in a [DCTERMS] conformsTo property. The value of this property must be an IRI [RFC3987] that references the standard or guidelines it follows.

The following example shows a conformance statement for an EPUB 3 Publication that conforms to the [DAISY Audio] guidelines.

<package …>
      <link rel="dcterms:conformsTo" href="http://www.daisy.org/guidelines/epub/navigable-audio-only-epub3-guidelines"/>

If the IRI is not sufficient for a user to understand conformance (e.g., the guidelines are not publicly available), more information about how the content has been optimized should be provided in the accessibility summary.


This specification does not define or recommend standards or guidelines for the production of optimized content. An informative registry of optimization standards is maintained separately from this specification, but no endorsement of them is implied.

  6 Distribution

The creation of an accessible EPUB Publication is not always enough to ensure that the content will be usable when it reaches users. Depending on how Authors distribute their content, other factors will influence the overall accessibility.

Some of these factors are outside the control of the Author, such as a third-party vendor's inaccessible bookstore or an inaccessible Reading system, but others can be ameliorated through careful distribution decisions.

For example, when distributing EPUB Publications, Authors can ensure that they do not impose digital rights management restrictions on their content that impair access by Assistive Technologies. They can also include accessibility metadata in distribution records so that it is available to vendors to use in bookstore search engines.

To ensure that EPUB Publications remain accessible to users, Authors must take all steps within their power to ensure that distribution of their content does not negatively affect its discoverability or usability. See Distribution Techniques [EPUB Accessibility Techniques] for more information.

  Appendix A. Authoring and Consumption

  A.1 Introduction

This section is informative

Although this specification focuses on content requirements for accessible EPUB Publications, there are two additional considerations in making EPUB Publications available to everyone: the ability for anyone to be able to create an EPUB Publication and the ability for anyone to consume the content.

Although these needs are not the primary focus of this specification, this appendix provides conformance requirements for the creation of accessible Authoring Tools and Reading Systems. Developers who meet or exceed these requirements will make their applications usable by a wide variety of users.


This appendix could be superseded by specifications dedicated to these concerns in the future.

  A.2 Authoring Tool Conformance

A conformant EPUB Authoring Tool must meet the following requirements:

  A.3 Reading System Conformance

A conformant Reading System must meet the following requirements:

  Acknowledgements and Contributors

This section is informative

EPUB has been developed by the International Digital Publishing Forum in a cooperative effort, bringing together publishers, vendors, software developers, and experts in the relevant standards.

The EPUB Accessibility specification and techniques were prepared by the International Digital Publishing Forum’s EPUB Maintenance Working Group, operating under a charter approved by the membership in July 2015, under the leadership of:

Work on these documents was undertaken by an accessibility subgroup led by:

Active members of the working group included:

IDPF Members

Invited Experts/Observers

For more detailed acknowledgements and information about contributors to each version of EPUB, refer to Acknowledgements and Contributors [EPUB3 Overview].


Normative References

[A11Y Test Suite] EPUB Accessibility Tests .

[ATAG 2.0] Authoring Tools Accessibility Guidelines (ATAG) 2.0 . Jan Richards, et al.

[Accessibility Vocab] EPUB Accessibility Vocabulary .

[DCTERMS] DCMI Metadata Terms .

[EPUB 3.1] EPUB 3.1 .

[Media Overlays] EPUB Media Overlays 3.1 .

[Packages] EPUB Packages 3 .

[RFC3987] Internationalized Resource Identifiers (IRIs) (RFC 3987) . M Duerst, et al. January 2005.

[UAAG 2.0] User Agent Accessibility Guidelines 2.0 . Ian Jacobs, et al. 17 December 2002.

[WAI-ARIA 1.1] Accessible Rich Internet Applications (WAI-ARIA) 1.1 . Joanmarie Diggs, et al.

[WCAG 2.0] Web Content Accessibility Guidelines (WCAG) 2.0 . Ben Caldwell, et al.

[WCAG 2.0 Techniques] Techniques for WCAG 2.0. . Michael Cooper, et al.

[schema.org] schema.org.

Informative References

[EPUB Accessibility Techniques] EPUB Accessibility Techniques .

[EPUB3 Overview] EPUB 3.1 Overview .