EPUB Accessibility 1.1

Conformance and Discoverability Requirements for EPUB Publications

W3C First Public Working Draft

This version:
Latest published version:
Latest editor's draft:
Matt Garrish (DAISY Consortium)
George Kerscher (DAISY Consortium)
Charles LaPierre (Benetech)
Gregorio Pellegrino (Fondazione LIA)
Avneesh Singh (DAISY Consortium)
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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.

Status of This Document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at https://www.w3.org/TR/.

This document was published by the EPUB 3 Working Group as a First Public Working Draft. This document is intended to become a W3C Recommendation.

GitHub Issues are preferred for discussion of this specification. Alternatively, you can send comments to our mailing list. Please send them to public-epub3@w3.org (subscribe, archives).

Publication as a First Public Working Draft does not imply endorsement by the W3C Membership.

This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

This document was produced by a group operating under the W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

This document is governed by the 15 September 2020 W3C Process Document.

1. Introduction

1.1 Overview

This section is non-normative.

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

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 accessible. At a minimum, all EPUB Publications that conform to this document meet the accessibility metadata requirements described in § 2. Discoverability.

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 § 3. Accessible Publications.

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 § 4. Optimized Publications.

This document 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 document.


For additional background on the decisions that went into this document, refer to EPUB Accessibility Frequently Asked Questions [AccessibilityFAQ].

1.2 Success Techniques

This section is non-normative.

This document takes an abstract approach to the accessibility requirements for EPUB Publications, similar to how WCAG [WCAG2] 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 [EPUB-A11Y-TECH-11] document outlines conformance techniques. These techniques explain how to meet the requirements of this document for different versions of EPUB.

1.3 Application to Older Versions

This section is non-normative.

This document is designed to be applicable to any EPUB Publication, even if the content conforms to an older version of EPUB that does not refer to this document (e.g., EPUB 2 [OPF-201]).

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.

1.4 Terminology

This document uses the following terminology defined in EPUB 3 [EPUB-3]:

In addition, it uses the definition of assistive technology as defined in [WCAG2].


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.

1.5 Conformance

As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.

The key words MAY, MUST, MUST NOT, RECOMMENDED, and SHOULD in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

2. Discoverability

2.1 Introduction

This section is non-normative.

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.

2.2 Package metadata

All EPUB Publications MUST include accessibility metadata in the Package Document that exposes their accessible properties, regardless of whether the publications also meet the accessibility or optimization requirements.

EPUB Publications MUST include the following accessibility metadata:

EPUB Publications SHOULD include the following accessibility metadata:

Authors MAY include additional accessibility metadata not specified in this section.


See Discovery Metadata Techniques [EPUB-A11Y-TECH-11] 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-A11Y-TECH-11] for more information on including accessibility metadata in other formats.

2.3 Linked Metadata Records

Accessibility metadata can also be included in linked records [EPUB-3] (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.

3. Accessible Publications

3.1 Introduction

This section is non-normative.

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) [WCAG2]. This document leverages the extensive work done in WCAG 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 section defines how to apply the conformance criteria defined in WCAG and 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.

3.2 Relationship to WCAG

This section is non-normative.

WCAG [WCAG2] and its associated 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 to an EPUB Publication — which is a collection of web documents as opposed to a single page — and adds an additional set of requirements. 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 [EPUB-A11Y-TECH-11]. 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 document will require an understanding of WCAG.

Because this document adds requirements that are not a part of WCAG, an EPUB Publication can conform to WCAG without conforming to this document.

3.3 WCAG conformance

3.3.1 WCAG Conformance Requirements

An EPUB Publication has to meet the following requirements to conform to this specification:

The reporting flexibility offered by these requirements is to ensure that this specification can be adapted for use wherever accessibility is mandated but without negating or superseding the requirements in effect in any region.

The baseline requirement for WCAG 2.0 Level A, for example, is primarily intended to provide Authors backwards compatibility for older content and flexibility to encourage adoption of accessible production where no formal requirements exist. It is not generally recognized as providing a high degree of accessibility.

Ideally, Authors should try to conform to the latest version of WCAG at Level AA, but the formal thresholds they must meet will be defined by local and national laws, or by procurer or distributor requirements.


Examples of legislative requirements for accessibility include the 2019 European Union (EU) Directive and Section 508 of the Rehabilitation Act of 1973 (United States). EPUB Publications will need to meet more than just the basic Level A success criteria to be compliant with these laws.

Keeping pace with WCAG has the benefit of continuously enhancing access for users. As web technologies change and improve, and awareness of conditions that impede access evolve, new requirements are added to the standard. Meeting these additional requirements helps ensure EPUB Publications employ the most up-to-date techniques. Meeting the requirements of older versions, while still helpful, can result in a less optimal reading experience.

Similarly, Level AA conformance is often cited as the benchmark for accessibility in legal frameworks and policies. The reason for this is that it provides the greatest range of improvements that can realistically be implemented (Authors are encouraged to try and meet the AAA requirements if they can, but fully conforming at AAA is typically not possible). Only meeting level A requires compromises for various user groups that can again result in a less optimal reading experience.

3.3.2 Evaluating WCAG Conformance Page and Publication

The WCAG principles [WCAG2] focus on the evaluation of individual web pages, but an EPUB Publication more closely resembles what WCAG refers to as a set of web pages: "[a] collection of Web pages that share a common purpose" [WCAG2].

Consequently, when evaluating the accessibility of an EPUB Publication, individual pages — or Content Documents, as they are known in EPUB 3 — cannot be reviewed in isolation. Rather, their overall accessibility as parts of a larger work also MUST be evaluated.

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

The WCAG 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 [EPUB-A11Y-TECH-11]. Applying the Conformance Criteria

When evaluating an EPUB Publication, the WCAG conformance criteria [WCAG2] are applied as follows:

  • When determining compliance with a conformance level, the whole EPUB Publication MUST meet the conformance requirements of the level claimed.
  • Authors MUST NOT use EPUB's fallback mechanisms to provide a conforming alternate version [WCAG2], 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. EPUB-specific fallback mechanisms include manifest fallbacks [EPUB-3], bindings [EPUB-3] and content switching via the epub:switch element [EPUB-3].
  • When determining compliance with the "Full Pages" requirement [WCAG2] (i.e., that parts of a page cannot be excluded when making a conformance claim), the entirety of each EPUB Content Document MUST achieve the conformance level and every Content Document in the EPUB Publication MUST meet the stated conformance level.

3.4 EPUB Requirements

3.4.1 Page Navigation Objective

Provide navigation to static page break locations. Understanding this Objective

This section is non-normative.

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, non-visual readers in an environment where statically paginated content is used are disadvantaged relative to their 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 dynamically paginated 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); or
  • 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.

A conformant EPUB Publication has to meet the following criteria 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 [EPUB-3]), Authors MUST identify the page numbers in the markup that controls the playback.


See Page Markers [EPUB-A11Y-TECH-11] for more information on the inclusion of page navigation in EPUB Publications. Relationship to WCAG

This section is non-normative.

The inclusion of page navigation represents one method of achieving the Multiple Ways success criterion [WCAG2], 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.

3.4.2 Media Overlays Playback Objective

Structure Media Overlays [EPUB-3] to provide more accessible playback experiences. Understanding this Objective

This section is non-normative.

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 [EPUB-3] 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 MUST meet the requirements in [EPUB-3]. It is not necessary to meet any additional requirements beyond those defined in [EPUB-3] to be conformant with this document.

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


This criterion does not require Authors to include Media Overlays in their EPUB Publications, only that they conform to these requirements when present. Relationship to WCAG

This section is non-normative.

Adding structure and semantics to Media Overlay Documents broadly falls under the objective of the Info and Relationships success criterion [WCAG2]. Without structured and semantically meaningful playback sequences, the effect is to deprive users of rich navigation of the content.

3.5 Conformance Reporting

Conformance reporting is achieved through the expression of metadata properties in the EPUB Package Document. The metadata uses a combination of properties from DCMI Metadata Terms [DCTERMS] and the EPUB Accessibility Vocabulary.

To indicate that an EPUB Publication conforms to the accessibility requirements of this document, it MUST include a conformsTo property in accordance with [DCTERMS] and an a11y:certifiedBy property.

The value of the conformsTo property MUST be one of the following URLs:

Issue 1455 : Reporting accessibility conformance Cat-AccessibilitySpec-Accessibility

The Working Group will replace these IDPF-based conformance URLs in a future update to this revision. The method of reporting may also change to reflect the increased flexibility around which version of WCAG has been met.


The EPUB Publication meets all accessibility requirements and achieves WCAG 2.0 Level A conformance [WCAG20].


The EPUB Publication meets all accessibility requirements and achieves WCAG 2.0 Level AA conformance [WCAG20].


The EPUB Publication meets all accessibility requirements and achieves WCAG 2.0 Level AAA conformance [WCAG20].


An EPUB Publication that only meets the content requirements of this document can report conformance using the WCAG conformance URL "http://www.w3.org/TR/2008/REC-WCAG20-20081211/" [WCAG20]. If accessibility metadata is supported through other means (e.g., ONIX records [ONIX]), its inclusion will further improve the discoverability of the publication.

The a11y:certifiedBy property specifies the name of the party that evaluated the EPUB Publication.


Conformance evaluation can be done by any individual or party. The evaluator can be the same party that created the EPUB Publication or a third party.


If an EPUB Publication is evaluated 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 organization, is generally discouraged, as it can diminish the trust the user has in the claim.

If the party that evaluates the content has been issued a credential or badge that establishes their authority to evaluate content, that information is supplied in an a11y:certifierCredential property.

If the party that evaluates the content has provided a detailed report of its assessment, a link to the assessment is provided in an a11y:certifierReport property.


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


This document does not define requirements for accessibility metadata external to an EPUB 3 publication as part of distribution metadata. Ensuring consistency between internal and external accessibility metadata expressions is the responsibility of authors, publishers, and distributors. For further discussion of the effects of distribution on accessibility, see § 5. Distribution.

4. Optimized Publications

Although WCAG [WCAG2] 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 because it is not designed for a broad audience.

For example, an EPUB Publication with synchronized text and audio can contain a full audio recording of the content but limit the text content to only the major headings. In this case, the EPUB Publication is consumable by users who needs to hear the content (i.e., they can listen to the full publication and can navigate between headings), but it is not usable by anyone who cannot hear the audio.

In other words, when an EPUB Publication is optimized for specific reading modalities, the failure to achieve a WCAG conformance level does not make it any less accessible to the intended audience.

An EPUB Publication that has been optimized MUST identify the standard or guidelines the content adheres to in a conformsTo property in accordance with [DCTERMS]. The value of this property MUST be a URL in accordance with [URL] that references the standard or guidelines it follows.

If the URL 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 document does not define or recommend standards or guidelines for producing optimized content. The informative EPUB Optimized Publication Standards Registry is maintained separately from this document, but no endorsement of the standards is implied.

5. Distribution

The creation of an EPUB Publication that is accessible does not in itself guarantee that the content will be obtainable or consumable by users. Depending on how the EPUB Publication is distributed, other factors will influence its overall accessibility.

Not all these factors are under the control of the Author. For example, an accessible interface for locating and obtaining content is an essential part of the distribution process, as is the ability to search and review accessibility metadata. Such interfaces are typically out of the control of content Authors, however, as distribution of EPUB Publications is often done through third parties. Even when an Author controls their own distribution, the accessibility of their bookstore, library and/or Reading System can be outside their control.

There are, however, decisions an Author can control when their content is distributed, such as what digital rights to apply to their EPUB Publications. Although these decisions are not part of the preparation of their EPUB Publications, their potential impact on users means attention needs to be paid to them.

To minimize the effects of distribution on accessibility, Authors are therefore advised to adhere to the following distribution practices:


A distributor may implement a digital rights management scheme that inherently impairs accessibility through no fault of the Author. Following the guidance in this section does not restrict Authors from using such distributors. The intent is that the Author does not impair accessibility by activating a feature that that would normally not be active (e.g., restricting access to the text by assistive technologies).

6. Privacy and Security

Editor's note

The working group will address issues related to privacy and security, if any, in a future draft.

A. EPUB Accessibility Vocabulary

A.1 Overview

A.1.1 About this vocabulary

This vocabulary defines properties for describing the accessibility of EPUB Publications in the Package Document metadata.

A.1.2 Referencing

The base URL for referencing this vocabulary is http://www.idpf.org/epub/vocab/package/a11y/#.

The prefix "a11y:" is reserved for use with properties in this vocabulary and does not have to be declared in the Package Document.

A.1.3 Conformance properties

A.1.3.1 certifiedBy
Name: certifiedBy
Description: Identifies a party responsible for the testing and certification of the accessibility of an EPUB Publication.
Allowed value(s): xsd:string
Cardinality: One or more
<meta property="a11y:certifiedBy">Accessibility Testers Group</meta>
A.1.3.2 certifierCredential
Name: certifierCredential
Description: Identifies a credential or badge that establishes the authority of the party identified in the associated certifiedBy property to certify content accessible.
Allowed value(s): xsd:string
Cardinality: Zero or more
Extends: a11y:certifiedBy
<meta property="a11y:certifiedBy" id="certifier">Accessibility Testers Group</meta>
<meta property="a11y:certifierCredential" refines="#certifier">DAISY OK</meta>
A.1.3.3 certifierReport
Name: certifierReport
Description: Provides a link to an accessibility report created by the party identified in the associated certifiedBy property.
Allowed value(s): xsd:anyURI
Cardinality: Zero or more
Extends: certifiedBy
<meta property="a11y:certifiedBy" id="certifier">Accessibility Testers Group</meta>
<link rel="a11y:certifierReport" refines="#certifier" href="http://example.com/a11y/reports/9780000000001"/>

B. Change Log

Note that this change log only identifies substantive changes — those that affect the conformance of EPUB Publications or are similarly noteworthy.

For a list of all issues addressed during the revision, refer to the working group's issue tracker.

B.1 Substantive changes since EPUB Accessibility 1.0

C. Acknowledgements

This section is non-normative.

The editors would like to thank the members of the EPUB 3 Working Group for their contributions to this specification:

D. References

D.1 Normative references

DCMI Metadata Terms. DCMI Usage Board. DCMI. 20 January 2020. DCMI Recommendation. URL: https://www.dublincore.org/specifications/dublin-core/dcmi-terms/
EPUB 3. W3C. URL: https://www.w3.org/publishing/epub3/
EPUB Accessibility Techniques 1.1. Matt Garrish; George Kerscher; Charles LaPierre; Gregorio Pellegrino; Avneesh Singh. W3C. 05 URL: https://www.w3.org/TR/epub-a11y-tech-11/
Key words for use in RFCs to Indicate Requirement Levels. S. Bradner. IETF. March 1997. Best Current Practice. URL: https://tools.ietf.org/html/rfc2119
Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words. B. Leiba. IETF. May 2017. Best Current Practice. URL: https://tools.ietf.org/html/rfc8174
URL Standard. Anne van Kesteren. WHATWG. Living Standard. URL: https://url.spec.whatwg.org/
Web Content Accessibility Guidelines (WCAG) 2. W3C. URL: https://www.w3.org/TR/WCAG2/
Web Content Accessibility Guidelines (WCAG) 2.0. Ben Caldwell; Michael Cooper; Loretta Guarino Reid; Gregg Vanderheiden et al. W3C. 11 December 2008. W3C Recommendation. URL: https://www.w3.org/TR/WCAG20/

D.2 Informative references

EPUB Accessibility Frequently Asked Questions. URL: http://www.idpf.org/epub/guides/a11y-faq
Navigable audio-only EPUB 3 Guidelines. URL: http://www.daisy.org/guidelines/epub/navigable-audio-only-epub3-guidelines
ONIX for Books 3.0. URL: https://www.editeur.org/8/ONIX/
Open Packaging Format 2.0.1. IDPF. 04 September 2010. URL: http://www.idpf.org/epub/20/spec/OPF_2.0.1_draft.htm