EPUB Accessibility 1.1

Conformance and Discoverability Requirements for EPUB Publications

W3C Working Draft

This version:
Latest published version:
Latest editor's draft:
Previous version:
Matt Garrish (DAISY Consortium)
George Kerscher (DAISY Consortium)
Charles LaPierre (Benetech)
Gregorio Pellegrino (Fondazione LIA)
Avneesh Singh (DAISY Consortium)
GitHub w3c/epub-specs
File an issue
Commit history
Pull requests


This specification 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/.

Editor's note

Publishers not currently producing accessible content are encouraged to begin updating their production processes to meet the requirements of [EPUB-A11Y-10] while this specification is being developed. Content that meets the requirements of that version will typically also meet the requirements of this specification with few changes necessary.

This document was published by the EPUB 3 Working Group as a 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 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 specification, 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 accessible certification. At a minimum, all EPUB Publications that conform to this specification meet the accessibility metadata requirements described in § 2. Discoverability.

Although EPUB Creators have always been able to create EPUB Publications with a high degree of accessibility, this specification sets formal requirements for certifying content accessible. These requirements provide EPUB Creators a clear set of guidelines to evaluate their content against and allows certification of quality. An accessible EPUB Publication is one that meets the accessibility requirements described in § 3. Accessible Publications.

The specification also establishes how to identify content that EPUB Creators have optimized for specific user needs so cannot meet broad accessibility requirements. Refer to the requirements for optimized publications in § 4. Optimized Publications for more information.

This specification does not target a single version of EPUB. It applicable to EPUB Publications that conform to any version or profile, including future versions of the standard.

Ideally, these guidelines help evaluate 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 EPUB Accessibility Frequently Asked Questions [AccessibilityFAQ].

1.2 Success Techniques

This section is non-normative.

This specification 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 specification for different versions of EPUB.

1.3 Application to Older Versions

This section is non-normative.

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

Creators of such EPUB Publications should create content in conformance with the accessibility and discoverability requirements of this specification. EPUB Creators should also upgrade to the latest version of EPUB to get access to the most advanced accessibility features and techniques.

1.4 Terminology

This specification 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, OPTIONAL, 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 Creators distribute EPUB Publications 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 must 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 any interested party can discover the accessible qualities of an EPUB Publication is therefore a primary concern. Users must 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 specification 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:

EPUB Creators 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 specification.

3. Accessible Publications

3.1 Introduction

This section is non-normative.

EPUB builds 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 Creators can author EPUB Publications with a high degree of accessibility simply through the proper application of established web accessibility techniques.

The primary source producing accessible web content is the W3C Web Content Accessibility Guidelines (WCAG) [WCAG2]. This specification 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 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 this specification does not call out those requirements, it does not diminish their importance in creating EPUB Publications that are accessible.

This specification 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. (Each requirement explains its relationship to WCAG 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 EPUB Creators can read this section without deep knowledge of WCAG conformance, to implement the accessibility requirements of this specification requires an understanding of WCAG.

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

3.3 WCAG Conformance

3.3.1 WCAG Conformance Requirements

To conform to this specification, an EPUB Publication:

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

This specification sets the baseline requirement to WCAG 2.0 Level A, for example, primarily to provide EPUB Creators backwards compatibility for older content and flexibility to encourage adoption of accessible production where no formal requirements exist. Most accessibility practitioners do not recognize this level as providing a high degree of accessibility, however.

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


Examples of legislative requirements for accessibility include the Directive 2019/882 in the European Union and Section 508 of the Rehabilitation Act of 1973 in the 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, the standard adds new requirements. 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, legal frameworks and policies often cite Level AA conformance as the benchmark for accessibility. The reason is that it provides the greatest range of improvements that EPUB Creators can realistically implement (EPUB Creators should try to meet the AAA requirements if they can, but fully conforming at AAA is typically not possible). When EPUB Creators meet only Level A conformance, they compromise their content for various user groups, resulting 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, EPUB Creators cannot review individual pages — or Content Documents, as they are known in EPUB 3 — in isolation. Rather, EPUB Creators MUST evaluate their overall accessibility as parts of a larger work.

For example, it is not sufficient for EPUB Creators to give individual EPUB Content Documents a logical reading order if they list the documents in the wrong reading order. Likewise, including a title for every EPUB Content Document is complementary to providing a title for the publication: the overall accessibility decreases if either is missing.

EPUB Creators MUST evaluate the WCAG guidelines for content to be perceivable, operable, understandable, and robust against the full EPUB Publication, not only against each Content Document within it.

The EPUB Accessibility Techniques [EPUB-A11Y-TECH-11] provide more information about applying these guidelines to EPUB Publications. 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.
  • EPUB Creators 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 an EPUB Creator uses fallbacks, 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 Overview

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 face disadvantages relative to their peers in environments that use statically paginated content as they cannot easily locate the same locations in a 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 the choice of reflowable media does not disadvantage those users.

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.

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 solely as one of many ways to meet the Multiple Ways success criterion.


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

An EPUB Publication SHOULD include the page navigation objectives defined in this section whenever any of the following cases is true:

  • the EPUB Creator identifies the EPUB Publication as the dynamically paginated equivalent of a statically paginated publication (e.g., included in a print/digital bundle);
  • the EPUB Creator offers the EPUB Publication as an alternative to a statically paginated publication in an environment where they can reasonably predict the use of both versions (e.g., educational settings); or
  • the EPUB Creator generates the EPUB Publication and a statically paginated publication from a workflow that allows the retention of page break locations across formats.

EPUB Creators MAY include page navigation in reflowable EPUB Publications without statically paginated equivalents. Objectives Pagination Source

Identify the source of static page break locations.

Understanding this Objective

Users need to know the source of the pagination in an EPUB Publication to determine whether it will be useful for their needs. Print publications, for example, produced in both hard and soft cover editions will have different pagination. Different editions of the same book often also have different pagination.

Including a recognizable identifier for the statically paginated source, such as its ISBN or ISSN, ensures that users can determine which version the pagination corresponds to.

If EPUB Creators insert pagination as a navigation aid for digital-only publications, they must not specify a source (i.e., do not identify the current publication as the source of its own pagination).

Meeting this Objective

When an EPUB Publication includes page break markers and/or a page list that correspond to a statically-paginated version of the publication, EPUB Creators MUST identify that source in the Package Document metadata. Page List

Provide navigation to static page break locations.

Understanding this Objective

The page list is the primary means of navigating to page break locations as it provides a list of links to each of the static page break locations in the EPUB Publication.

Reading Systems typically use this list to generate a "go to page" interface in which users can plug in the page number that they wish to move to, but sometimes offer users the ability to access the full list and select the page number to go to.

Without a page list, page navigation becomes extremely difficult as it would rely on navigating the individual page break markers (if they are even present).

Meeting this Objective

An EPUB Publication MUST include a page list.

EPUB Creators SHOULD include links to all pages of content reproduced from the source (i.e., they do not have to provide links for blank pages or content not reproduced in the digital edition).

EPUB Creators should include links for all pages in the source whether they are reproduced or not, but this is not a requirement. Page Breaks

Provide static page break locations.

Understanding this Objective

Inserting page breaks markers into an EPUB Publication provides users with context about where they are in the text. Assistive technologies can use this information to announce the current page number the user is on, for example, if the user wants to cite something on the page.

The inclusion of page break markers can also allow users to move quickly forwards and backwards by page without having to access the page list each time.

The inclusion of these markers also simplifies the creation a page list, as they provide easily referenced destinations for the links.

Meeting this Objective

Inclusion of page break markers in an EPUB Publication is OPTIONAL.

If an EPUB Creator includes page break markers:

  • they SHOULD include page break markers for all pages reproduced from the source (i.e., blank pages and content not reproduced in the digital edition do not require markers).
  • they should include page break markers for all pages in the source (whether reproduced or not), but this is not a requirement.

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]), EPUB Creators MUST identify the page numbers in the markup that controls the playback.

3.4.2 Media Overlays Playback Overview

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.

EPUB Creators 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.

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. Applicability

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 specification.

To maximize the effectiveness of Media Overlays for people with different reading needs, however, EPUB Creators are strongly encouraged to meet the OPTIONAL objectives defined in the next section.


EPUB Creators do not have to include Media Overlays in their EPUB Publications, only ensure they conform to these requirements when present. Objectives Completeness

Ensure that the full text is available in audio.

Understanding this Objective

Although it is possible for users who require a publication in audio form to use text-to-speech playback, the experience is considerably poorer than when pre-recorded narration is provided. Text-to-speech engines have limited built-in vocabularies, causing them to mangle and mispronounce most uncommon words they encounter. As a reult users have to have words repeated and spelled out to make sense of the content, slowing down their reading and reducing comprehension.

For this reason, it is important to provide narration for the full text of a publication in addition to the full text. Users can then decide which reading modality they prefer — text, audio, or a mix of the two.

Meeting this Objective

EPUB Creators MUST provide synchronized audio playback via Media Overlays for all textual content. Reading Order

Ensure Media Overlay playback matches logical reading order.

Understanding this Objective

Every EPUB Publication has a default reading order that allows users to logically progress through the content. It ensures that readers can follow the primary narrative and that they encounter secondary content where it makes the most sense. The default reading order also establishes some less obvious relations, like the progress within a table from cell to cell and row to row.

If the sequence of par and seq elements in a Media Overlay Documents does not match this progression, it can cause confusion for readers, whether they are only listening to the audio or trying to also follow visually.

Ordering the playback to match the default reading order is the safest way to ensure that users can follow the text. In some cases, however, strict adherence to this practice could result in a suboptimal reading experience (e.g., playback of a table by column instead of row might make more logical sense in some cases). The goal of this objective is not to forbid alternate presentations, but to ensure that any deviations retain the logical flow of the content.

Meeting this Objective

EPUB Creators SHOULD order the par and seq elements in a Media Overlays Document such that they reflect both:

  • the order of the referenced EPUB Content Documents in the spine [EPUB-3]; and
  • the order of each element within its respective EPUB Content Document.

If EPUB Creators use a different ordering, that ordering MUST still result in a logical playback of the content. Skippability

Enable users to automatically skip over content.

Understanding this Objective

Being able to read the primary narrative of a work without interruption is central to reading comprehension. EPUB Creators typically structure EPUB Publications to visually represent secondary information such as sidebars and footnotes outside the main narrative flow (e.g., by using different background colours or placement so readers can filter this information visually out while reading).

Readers who prefer auditory playback, however, cannot skip this information with the same ease by default. Media overlays playback will typically result in Reading Systems rendering secondary content where it occurs.

When EPUB Creators add structural semantics to Media Overlay Documents, however, Reading Systems can create reading experiences that allow users to decide which secondary content to skip by default during playback.

Meeting this Objective

EPUB Creators SHOULD identify all skippable structures [EPUB-3] in Media Overlay Documents. Escapability

Enable users to automatically escape from structured content.

Understanding this Objective

When reading visually, users can quickly move through, and escape from, highly structured content such as tables, lists, and figures. Table layouts that use rows and columns, for example, allow users to quickly move along either axis to find the information they want, and to easily return to the primary narrative when they finish. Similarly, lists of items allow users to skim their content and escape from them once they locate the desired information.

The same ease of escaping from content is not available in Media Overlay Documents by default. Users cannot escape from table cells, rows, or even the table itself, unless EPUB Creators encode the structural semantics of those elements in the document.

When EPUB Creators provide this information, Reading Systems can simplify playback for auditory readers to enable a comparable reading experience.

Meeting this Objective

EPUB Creators SHOULD identify all escapable structures [EPUB-3] in the Media Overlay Documents. Navigation Document

Ensure auditory playback is possible for the navigation aids in the EPUB Navigation Document when presented by Reading Systems.

Understanding this Objective

Reading Systems typically provide their own interfaces to the navigation aids in the EPUB Navigation Document. For example, they open the table of contents as a specialized interface on top of the content the user is reading.

To access these interfaces, users typically must rely on text-to-speech playback, when available, to hear the entries.

Providing a Media Overlay Document for the EPUB Navigation Document provides Reading Systems the ability to use auditory labels for the links, improving the experience for auditory readers.

Meeting this Objective

EPUB Creators SHOULD include a Media Overlay Document for the EPUB Navigation Document [EPUB-3].

3.5 Conformance Reporting

3.5.1 Introduction

This section is non-normative.

Evaluators report the accessibility conformance of an EPUB Publication through the expression of metadata properties in the EPUB Package Document.

This metadata establishes both:

The metadata uses a combination of properties from DCMI Metadata Terms [DCTERMS] and the EPUB Accessibility Vocabulary, as explained in more detail in the following sections.

3.5.2 Publication Conformance

To indicate that an EPUB Publication conforms to the accessibility requirements of this specification, it MUST include a conformsTo property whose value MUST exactly match (i.e., both in case and spacing) the following pattern:




EPUB Creators MUST specify the version number of the EPUB Accessibility specification the publication conforms to, not including the decimal points. EPUB Creators MUST use the value 11 to indicate this version of this specification.


EPUB Creators MUST specify the version number of WCAG the publication conforms to, not including the decimal points (e.g., 20 for WCAG 2.0 or 21 for WCAG 2.1).


EPUB Creators MUST specify the WCAG conformance level the publication conforms to (e.g., A or AA).

The following conformance strings are valid as of publication of this specification:

  • EPUB-A11Y-11_WCAG-20-A
  • EPUB-A11Y-11_WCAG-20-AA
  • EPUB-A11Y-11_WCAG-20-AAA
  • EPUB-A11Y-11_WCAG-21-A
  • EPUB-A11Y-11_WCAG-21-AA
  • EPUB-A11Y-11_WCAG-21-AAA

The list of valid conformance strings will increase as W3C releases new versions of WCAG.


The future 3.0 version of WCAG is likely to also introduce new level names (currently Bronze, Silver and Gold). Those names would replace A, AA, and AAA in the string pattern.


An EPUB Publication that only meets WCAG conformance requirements (i.e., does not fully conform to this specification) can use a WCAG conformance URL (e.g., "https://www.w3.org/TR/WCAG21/" for [WCAG21]) with the confomsTo property.

3.5.3 Evaluator Information

EPUB Publications MUST include an a11y:certifiedBy property that specifies the name of the party that evaluated the EPUB Publication.


Any individual or party can perform a conformance evaluation. The evaluator can be the same party that created the EPUB Publication or a third party.


If an organization evaluates an EPUB Publication, users will typically want to know the name of that organization. This specification discourages including the name of the individual(s) who carried out the assessment, instead of the name of the organization, as this can diminish the trust users have in the claim.

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

If the party that evaluated the content provides a publicly-readable report of its assessment, provide a link to the assessment in an a11y:certifierReport property.


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


This specification 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.

3.5.4 Re-Evaluating Conformance

This section is non-normative.


The following guidance is to help EPUB Creators determine when a new evaluation is necessary. It is not a requirement to conform to this specification.

How long a conformance evaluation of an EPUB Publication is good for is complex question. Unlike web sites, which are continuously evolving, an EPUB Creators may never update an EPUB Publication after its initial publication. As a result, an unmodified EPUB Publication will always conform to its last evaluation.

It is common in publishing, however, to release updated versions of an EPUB Publication to fix errors and typos in the work, as well as to periodically release new editions. As not all changes to an EPUB Publication substantively change its accessibility, this complicates the question of when EPUB Creators should perform a new evaluation, as well as whether a full or partial re-evaluation will suffice.

As a rule, EPUB Creators must re-evaluate their content whenever they make substantive changes to the structure and functionality of an EPUB Publication, such as:

  • modifications to the nature or order of markup in EPUB Content Documents;
  • additions or modifications to images that convey information;
  • modifications to formatting that affects the readability (e.g., contrast); and
  • additions or modifications to interactive controls, forms, etc.

If the EPUB Publication includes substantively the same markup and content as the previous release, the EPUB Creator may only need to evaluate the new modifications to re-confirm conformance.

If an updated version of this specification or [WCAG] has been published since the last release of the EPUB Publication, however, this specification also recommends performing a new evaluation to ensure conformance to the latest standards. EPUB Creators may not have to perform a full re-evaluation even in this case (i.e., they may only need to check new or modified success criteria unless the standards undergo major changes to methodology or conformance).

Conversely, EPUB Creators do not need to perform a re-evaluation when making non-substantive changes, such as:

  • fixes for typographic errors in the text (i.e., no markup is changed);
  • additions or modifications to decorative images;
  • modifications to the formatting that do not affect the understanding of the content or change the text display; and
  • modifications to Package Document metadata.

Individuals qualified to assess the accessibility of EPUB Publications should make the determination of whether changes are substantive or not. An editor, for example, may not realize the impact of seemingly minor formatting changes.

Even in the case of non-substantive changes, this specification recommends an updated evaluation (full or partial) if the accessibility standards have changed.

EPUB Creators should consider even more progressive approaches than those described here. Waiting for content changes before reviewing and updating the accessibility of EPUB Publications can leave them lacking recent improvements. For example, a publisher might prioritize periodic reviews of their top-selling EPUB Publications to ensure they remain maximally usable to the widest possible audience.

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 exactly because it targets a specific 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 EPUB Creators optimize an EPUB Publication for specific reading modalities, the failure to achieve a WCAG conformance level does not make it any less accessible to the intended audience.

EPUB Creators MUST identify the standard or guidelines that an optimized EPUB Publication adheres to in a conformsTo property in accordance with [DCTERMS]. For the value, EPUB Creators MUST specify a URL, in accordance with [URL], that references the standard or guidelines the content 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 specification does not define or recommend standards or guidelines for producing optimized content. For an informative list of such standards, however, refer to the EPUB Optimized Publication Standards Registry.

5. Distribution

This section is non-normative.


Although EPUB Creators do not have to follow the recommendations in this section to conform to this specification, some jurisdictions require EPUB Creators to follow similar practices. Directive 2019/882, for example, includes similar requirements for digital publications distributed in the European Union.

The creation of accessible EPUB Publications does not guarantee that the publication will be obtainable or consumable by users in an accessible fashion. Depending on how EPUB Creators distribute their EPUB Publications, other factors will influence their overall accessibility. 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.

While much of the distribution process is outside the control of EPUB Creators, so outside the scope of this specification, there are factors an EPUB Creator can control. For example, while an EPUB Creator typically does not control the accessibility of the digital rights management (DRM) scheme applied to their EPUB Publications, they do control what usage rights to apply to their EPUB Publications. So even though a DRM scheme may allow an Author to block access to the text of the publication, the EPUB Creator needs to take care not to apply such a restriction as it could block the ability for assistive technologies to read the text aloud.

To minimize the effects of distribution on accessibility, this specification advises EPUB Creators adhere to the following distribution practices:


A distributor may implement a digital rights management scheme that inherently impairs accessibility through no fault of the EPUB Creator. Following the guidance in this section does not restrict EPUB Creators from using such distributors. The intent is only that the EPUB Creator not impair accessibility by activating a feature that that would normally not be active.

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/#.

This specification reserves the prefix "a11y:" for use with properties in this vocabulary. EPUB Creators do not have to declare the prefix 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

This section is non-normative.

Note that this change log only identifies substantive changes since EPUB Accessibility 1.0 — 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.

C. Acknowledgements

This section is non-normative.

The following members of the EPUB 3 Working Group contributed to the development of 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/TR/epub/
Key words for use in RFCs to Indicate Requirement Levels. S. Bradner. IETF. March 1997. Best Current Practice. URL: https://www.rfc-editor.org/rfc/rfc2119
Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words. B. Leiba. IETF. May 2017. Best Current Practice. URL: https://www.rfc-editor.org/rfc/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
EPUB Accessibility 1.0. Matt Garrish; George Kerscher; Charles LaPierre; Avneesh Singh. IDPF. 05 January 2017. URL: http://idpf.org/epub/a11y/accessibility-20170105.html
EPUB Accessibility Techniques 1.1. Matt Garrish; George Kerscher; Charles LaPierre; Gregorio Pellegrino; Avneesh Singh. W3C. 3 September 2021. W3C Note. URL: https://www.w3.org/TR/epub-a11y-tech-11/
MARC 21 XML. URL: https://www.loc.gov/standards/marcxml/
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
Web Content Accessibility Guidelines 1.0. Wendy Chisholm; Gregg Vanderheiden; Ian Jacobs. W3C. 5 May 1999. W3C Recommendation. URL: https://www.w3.org/TR/WAI-WEBCONTENT/
Web Content Accessibility Guidelines (WCAG) 2.1. Andrew Kirkpatrick; Joshue O'Connor; Alastair Campbell; Michael Cooper. W3C. 5 June 2018. W3C Recommendation. URL: https://www.w3.org/TR/WCAG21/