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. 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/.
W3C recommends the wide deployment of this specification as a standard for
the Web.
A W3C Recommendation is a specification that, after extensive
consensus-building, is endorsed by
W3C and its Members, and
has commitments from Working Group members to
royalty-free licensing
for implementations.
Future updates to this Recommendation may incorporate
new features.
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 specification, EPUB Accessibility, addresses two key needs in the EPUB ecosystem:
discoverability of the accessible qualities of EPUB publications; and
evaluation and certification of accessible EPUB publications.
The provision of accessibility metadata facilitates informed decisions about the usability of an EPUB
publication. Consumers can review the qualities of the content and decide whether an EPUB
publication is appropriate for their needs, regardless of whether it meets the bar of 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 discusses the practice of optimizing EPUB publications for specific reading
modalities. In these cases, the content cannot meet the broad accessibility requirements of this
specification, but by following its discoverability and reporting requirements EPUB creators can
improve the ability of users to determine if the content still meets their needs. Refer to 4. Optimized publications for more information.
The specification also addresses the impact of distribution on the accessibility and discoverability
of content in 5. Distribution.
This specification does not target a single version of EPUB. It is 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 Platform
technologies, although ensuring such application is outside the scope of this specification.
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.
1.2.1 Internationalization
This specification is also designed to address the accessibility needs of users independent of
what languages they read. The same is true for the principles and success criteria defined in
[wcag2]. The goal is to ensure that users can fully consume the information of a publication
regardless of their preferred reading modality.
At the same time, the language and writing conventions of the authored text will influence the
techniques necessary to meet the accessibility requirements. EPUB requires support for Unicode text
[epub-3], for example, which ensures the correct character data can be used (i.e., EPUB creators do not have to use
images of text). Although this is an important feature, it is often not enough on its own to
ensure that the text is fully accessible in any given language (e.g., additional information
about directionality, emphasis, pronunciation, etc. may also be needed).
As a consequence, there may be language- or culture-specific practices for meeting accessibility
requirements. Whether these practices are defined within this specification and its techniques
or elsewhere (e.g., in WCAG techniques or language-specific best practice recommendations) will
depend on whether the issues are specific to EPUB or broadly affect all web content.
1.3 Application to older versions
This section is non-normative.
This specification is 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.
Note that not all metadata expressions defined in this specification are supported in older version
of EPUB. EPUB 2, in particular, does not support the refines attribute
[epub-3]. If EPUB creators cannot avoid expressions that require this attribute, they will have to
accept a certain amount of ambiguity in their statements (i.e., relationships between expression may
only be apparent by their placement in the package document metadata).
In the case of EPUB, 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.
Note
Only the first instance of a term in a section links to its definition.
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, SHOULD, and SHOULD NOT 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. An EPUB publication can have more than one set of sufficient access modes depending on the alternatives provided to
enable reading in another mode. For example, if alternative text and descriptions are provided for
all the images in a publication, it would have both its default textual and visual sufficient access
mode and a purely textual sufficient access mode.
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.
EPUB publications MUST include the following accessibility metadata:
accessMode — a
human sensory perceptual system or cognitive faculty necessary to process or perceive the
content (e.g., textual, visual, auditory, tactile).
accessibilityFeature — features and adaptations that contribute to 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).
EPUB publications SHOULD include the following [schema-org] accessibility metadata:
accessibilitySummary — a human-readable summary of the accessibility that
complements, but does not duplicate, the other discoverability metadata. The summary also
describes any known deficiencies (e.g., lack of extended descriptions, specific
hazards).
accessModeSufficient — a set of one or more access modes sufficient to consume the
content without significant loss of information. An EPUB publication can have more than one
set of sufficient access modes for its consumption depending on the types of content it
includes (i.e., unlike access modes, this property
takes into account any alternatives for content that is not broadly accessible, such as the
inclusion of transcripts for audio content).
EPUB creatorsMAY include additional
[schema-org] accessibility metadata not specified in this section.
Note
This specification assumes that conformance and discoverability metadata will be processed and
presented in a human-readable manner, removing the need for a summary unless there is additional
information to express. Such processing is not available in all market segments, however,
particularly in library systems. Publishers should consider this limitation when deciding
whether to include a summary and what to state in it.
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. Leveraging these technologies allows EPUB creators to author EPUB publications with a high degree
of accessibility through the application of established web accessibility techniques, such as using
native elements and controls whenever possible and enhancing custom interactive content with
[wai-aria] roles, states, and properties. Plus, whenever possible, the EPUB community adds
publishing accessibility needs to these standards — for example, through the creation of the
[dpub-aria-1.0] role module. It is not necessary for anyone familiar with web accessibility to
learn a new accessibility framework to make EPUB publications accessible.
The primary source for producing accessible web content is the W3C's Web Content Accessibility
Guidelines (WCAG) [wcag2], which establish benchmarks for accessible content. WCAG defines four
high-level content principles — that content be perceivable, operable, understandable, and robust.
These principles are also central to creating accessible EPUB publications, so it is no surprise
that this specification builds on the extensive work done in WCAG.
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, covering
everything from multimedia to interactive content to structured markup and more. 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.
MUST, at the minimum, meet the requirements of WCAG 2.0 [wcag20],
but it is strongly recommended that it meet the requirements of the latest recommended version of WCAG 2.
MUST, for whichever version of WCAG 2 selected, meet the requirements
of Level A, but it is strongly recommended that it meet
the requirements of Level AA.
Note
Although conforming at level AAA is not required by
this specification, EPUB
creators are encouraged to follow the practices detailed in AAA success
criteria when producing accessible EPUB publications.
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 2 at Level AA, but
local and national laws, or procurer or distributor requirements, will define the formal
thresholds they must meet.
Note
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. When EPUB creators meet only Level A conformance, they
compromise their content for various user groups, resulting in a less optimal reading
experience.
Note
The W3C Accessibility Guidelines Working Group is
currently developing WCAG 3. As this version potentially represents a significant departure
from WCAG 2, a future version of this specification will address conformance requirements
related to it. EPUB creators are encouraged to adopt WCAG 3 once it is stable and widely
recognized, but conformance to the new version is not a requirement of this standard.
3.3.2 Evaluating WCAG conformance
3.3.2.1 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 EPUB content documents, as they are known in EPUB 3 — in isolation.
Rather, EPUB creators MUST evaluate their accessibility as part of the larger work.
For example, it is not sufficient for EPUB creators to order the content within individual EPUB content documents
if they list the documents in the wrong order in the spine. 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 EPUB
content document within it.
The EPUB Accessibility Techniques [epub-a11y-tech-11] provide more information about
applying these guidelines to EPUB publications.
When determining compliance with a conformance level, the whole EPUB publication MUST
meet the conformance requirements of the level claimed.
EPUB creatorsMUST 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].
The "Full Pages" requirement [WCAG2] -- that parts of a
page cannot be excluded when making a conformance claim -- applies to every EPUB content
document in the EPUB publication (i.e., they must all conform in full to the
conformance level claimed).
3.4 EPUB requirements
3.4.1 Page navigation
3.4.1.1 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.
An EPUB publicationSHOULD
include page navigation 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.
When EPUB creators include page navigation, the objectives defined in this section apply to
the EPUB publication.
3.4.1.3 Objectives
3.4.1.3.1 Pagination source
Objective
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.
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 creatorsSHOULD
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 MUST include links to all page break
markers in the content.
EPUB creators should include links for all pages in the source whether they are
reproduced or not, but this is not a requirement.
Inserting page break 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 of 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.
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.
The provision of synchronized text-audio playback helps address various user needs. It not
only enables a seamless visual and auditory reading experience from beginning to end of an
EPUB publication, but is
useful to users who only require audio playback (e.g., who cannot see the text or are
prevented from reading visually due to motion-sickness) or who only benefit from reading
with text highlighting (e.g., readers with dyslexia).
Unlike purely linear listening experiences, EPUB with synchronized text-audio playback
preserves the user's ability to navigate around the publication, such as via the table of
contents, and also introduces audio-centric reading features like phrase navigation, and
ways to control which parts of the content are read aloud.
In order to offer users greater control over content presentation, EPUB creators need to add
structure and semantics so that the reading system has the
necessary context to enable this type of user experience. With greater context, a reading
system can provide the ability to skip past secondary content that interferes with the
primary narrative and escape users from deeply nested structures like tables.
Adding structure and semantics to synchronized text-audio playback 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.
3.4.2.2 Applicability
EPUB publications with
synchronized text-audio playback MUST conform to all 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 synchronized text-audio playback for people with different
reading needs, however, EPUB
creators are strongly encouraged to meet the OPTIONAL
objectives defined in the next section.
Note
EPUB creators do not have to include synchronized text-audio playback in their EPUB
publications, only ensure it conforms to these requirements when present.
3.4.2.3 Objectives
3.4.2.3.1 Completeness
Objective
Ensure that all text content 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 result 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 creatorsMUST
provide synchronized audio playback for all visible textual content as well as
all textual alternatives for visual media.
Every EPUB
publication has a default reading order that allows users to progress
through the content. The default reading order consists of two parts: the order
of references in the spine provides a high-level progression through the EPUB content
documents that make up the publication, while the markup within each
EPUB content document provides the default progression through the content
elements (i.e., as represented in the document object model [dom]).
For many languages, the default reading order also matches the logical reading
order — the way that users will naturally follow the narrative. It ensures
that readers can follow the primary narrative and that they encounter secondary
content where the author intended it to be read. 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 the synchronized text-audio playback 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 can result in a suboptimal reading experience (e.g., playback
of a table by column instead of row might make more natural sense in some
cases). These publications have a logical reading order that cannot match the
default order of the elements of the host format.
The goal of this objective is not to forbid alternate presentations, but to
ensure that deviations are only made to better represent the logical reading
order of the content.
Meeting this Objective
EPUB creatorsSHOULD
order the synchronized text-audio playback instructions such that they reflect
both:
the order of the referenced EPUB content documents in the spine; 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.
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
page break markers and footnotes outside the main narrative flow (e.g., by using
different background colors 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 in a linear audio-based reading experience. And, without
structural semantics, synchronized text-audio playback cannot offer skipping
content either.
When EPUB creators add structural semantics, 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.
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 sidebars, lists, and figures. Visual readers can skim
lists and quickly return to the primary narrative once they locate the desired
information, for example. The same is true for reading figures and sidebars, as
they are visually offset from the primary narrative so easily jumped into and
out of.
The same ease of escaping from content is only possible if EPUB creators encode
the structural semantics into the synchronized text/audio format. Users may not
be able to escape from lists, sidebars, figures, and other highly structured
content, unless EPUB creators encode the structural semantics of those
elements.
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.
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 synchronized text-audio playback for the EPUB navigation document
provides reading systems the ability to use auditory labels for the links,
improving the experience for auditory readers.
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.
Although any individual or party can perform a conformance evaluation — provided they have
the knowledge and tools to assess EPUB publications against the WCAG and EPUB requirements of this specification —
users need to be able to trust that evaluations are performed in a comprehensive manner and that
conformance claims are not influenced by self-interest in the outcome.
To address this confidence issue, some regions designate a local authority responsible for all
evaluations, in which case there is no flexibility in who can perform evaluations. Where such
authorities do not exist, evaluators are encouraged to obtain and reference any applicable credentials to strengthen public confidence in their
evaluations.
Note
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.
Ensuring consistency between internal and external accessibility metadata expressions is the
responsibility of authors, publishers, and distributors. Refer to 5. Distribution for for a discussion of the effects of distribution on
accessibility.
Specifies the version number of the EPUB Accessibility specification the publication
conforms to. The value MUST be 1.1 or higher.
WCAG-VER
Specifies the version number of WCAG the publication conforms to. The value MUST be
2.0 or higher.
WCAG-LVL
Specifies 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 Accessibility 1.1 - WCAG 2.0 Level A
EPUB Accessibility 1.1 - WCAG 2.0 Level AA
EPUB Accessibility 1.1 - WCAG 2.0 Level AAA
EPUB Accessibility 1.1 - WCAG 2.1 Level A
EPUB Accessibility 1.1 - WCAG 2.1 Level AA
EPUB Accessibility 1.1 - WCAG 2.1 Level AAA
EPUB Accessibility 1.1 - WCAG 2.2 Level A
EPUB Accessibility 1.1 - WCAG 2.2 Level AA
EPUB Accessibility 1.1 - WCAG 2.2 Level AAA
Note
The list of valid conformance strings will increase as W3C releases new versions of WCAG.
In addition, WCAG 3.0 is set to introduce new
level names (currently Bronze, Silver and Gold). Those names will likely replace A, AA, and
AAA in the string pattern, but conformance will be addressed after that specification
becomes a W3C
Recommendation.
3.5.2.1 Other conformance claims
This section is non-normative.
The requirement to include a dcterms:conformsTo identifier does not prevent EPUB
publications from conforming to other standards, including other accessibility standards and
guidelines (e.g., a specification that covers specific natural language issues). An EPUB
publication can have multiple dcterms:conformsTo statements.
For example, if an EPUB publication only meets WCAG conformance requirements (i.e., does not
fully conform to this specification), EPUB creators can add a
dcterms:conformsTo property with a conformance URL defined in the Required Components of a
Conformance Claim [wcag2].
Note
As [wcag2] does not define how to specify the conformance level in the URL, EPUB
creators will have to find an alternative means of relating this information when
necessary (e.g., through the accessibility summary).
Conversely, EPUB creators might need to indicate that an EPUB publication does not meet any
accessibility standards (e.g., in order to claim an exemption). In these cases, they can use
a dcterms:conformsTo property with value "none".
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.
The following guidance is provided only to help EPUB creators determine when a
new evaluation is necessary. It is not a conformance requirement of this specification.
How long a conformance evaluation of an EPUB publication is good for is
a complex question. Unlike web sites, which are continuously evolving, EPUB creators may not
update EPUB publications after their 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:
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 [wcag2] 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
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
This section is non-normative.
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 an EPUB creator optimizes
an EPUB publication for a specific reading modality, the failure to achieve a WCAG conformance level
does not make it any less accessible to the intended audience.
Defining requirements for optimized publications is outside the scope of this specification, as is
formally recognizing other standards and guidelines that address these specific needs. The general model
of this specification can be used as a basis for identifying how an EPUB creator has optimized their
content, however.
In particular, if an EPUB publication meets the requirements of an optimization standard, the following
best practices are recommended:
The EPUB publication should meet the discovery metadata requirements of
this specification so its accessible properties are machine-readable.
The EPUB publication should identify the standard or guidelines it follows in a
conformsTo property in accordance with [dcterms] so this information can be made
available to users.
If the standard does not define conformance values for the conformsTo property, EPUB
creators should use a URL [url] to where the standard is publicly available so users can look up
the specific details of the standard.
If the identifier is not sufficient for a user to understand conformance (e.g., the guidelines are
not publicly available), EPUB creators should provide additional information about they have
optimized the content in the accessibility
summary.
When creating guidelines for optimized EPUB publications, it is recommended that these practices be
integrated as a formal requirement for conformance.
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:
they must not impose restrictions that impair access by assistive technologies; and
they must include accessibility metadata in the record format required for distribution of an EPUB
publication (e.g., [onix] or [marc21]) when the format supports such metadata.
Note
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 would normally not be active.
6. Privacy and security
The authoring of accessible content does not introduce any new privacy or security considerations for
users. Meeting accessibility requirements is about optimally using the available technologies, and no
new features are introduced by this specification.
The inclusion of accessibility metadata by EPUB
creators similarly does not introduce security or privacy issues for the EPUB creator, as
describing an EPUB publication only
provides a general idea of its suitability for different user groups.
The use of accessibility metadata in reading systems, bookstores and any other interface that can build a profile of the user, on
the other hand, has the potential to violate the user's privacy. While it might seem helpful to store
and anticipate the type of content a user is most likely to consume, for example, or how best to
initiate its playback, developers should not engage in such profiling unless explicit permission is
obtained from the user and a means of easily removing the profile is available.
Even in the case where a user assents to the application maintaining information about their
accessibility needs, developers SHOULD ensure that this information is kept private (e.g., not share the
information with third party advertisers or even with the original publisher).
Developers SHOULD NOT store or mine information about the types of searches a user performs when
searching for content based on its accessibility characteristics. This information can be used to
indirectly profile the abilities of users.
The base URL for referencing this vocabulary is
http://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 Certifier properties
A.1.3.1 certifiedBy
Definition of the certifiedBy property
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
Example:
<metaproperty="a11y:certifiedBy">
Accessibility Testers Group
</meta>
A.1.3.2 certifierCredential
Definition of the certifierCredential property
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
Example:
<meta
property="a11y:certifiedBy"
id="certifier">
Accessibility Testers Group
</meta>
<meta
property="a11y:certifierCredential"
refines="#certifier">
DAISY OK
</meta>
A.1.3.3 certifierReport
Definition of the certifierReport property
Name:
certifierReport
Description:
Provides a link to an accessibility report created by the party identified in the
associated certifiedBy property.
Note that this change log only identifies substantive changes since EPUB Accessibility 1.0 — those that may affect the conformance of EPUB publications.
12-Aug-2022: Changed accessibilitySummary from a required to a recommended property
and updated its definition to focus less on repeating information available in the other
metadata. See issue 2399.
12-Aug-2022: Changed the conformance identifier for publications to be more human-readable while
still machine-processable so that the information is not needlessly duplicated in the summary.
See issue 2398.
07-June-2022: Updated privacy and security recommendations to use normative language.
17-May-2022: Added an index of terms. See issue 2260.
12-Apr-2022: Restored recommendation to include links to all reproduced pages in the page list
and added a requirement to link to all page break markers to address concerns with the previous
change. Clarified that meeting the page navigation requirements is required, but adding page
navigation is only recommended in some circumstances. See pull request 2246.
12-Apr-2022: Generalized discussion of synchronized text-audio playback objectives and moved
specific details of using media overlays to the techniques document. See issue 2221.
08-Apr-2022: Changed the recommendation to include links to all reproduced pages in the page
list to a requirement. See issue
2220.
23-Mar-2022: Clarified linking for WCAG conformance versions and levels. See issue 2099.
21-Mar-2022: Note that not all metadata expressions can be achieved in EPUB 2 due to the absence
of the refines attribute. See issue 2042.
28-Sep-2021: The section on optimized publication has been made non-normative and rewritten to
highlight best practices for identifying conformance to such standards. See pull request 1833.
23-Sep-2021: Added section explaining effects of internationalization on techniques used. See issue 1790.
07-Sep-2021: Added refines attribute to certifier metadata examples to show the
expected linkage. See issue
1789.
07-Sep-2021: Added explanation that the dcterms:date property can be used to
indicate when an evaluation was performed. See issue 1590.
09-June-2021: Clarified that a pagination source must not be specified when page break markers
and/or a page list are included in a digital-only publication. See issue 1599.
29-Apr-2021: Change conformance identifiers to use hyphens and dashes so they are not confused
for plain language strings. See issue
1455.
26-Mar-2021: Added non-normative section detailing when to re-evaluate EPUB publications. See issue 1470.
12-Mar-2021: Changed the distribution section to non-normative but added a note that the
requirements must be followed where required by law (e.g., in the EU). See issue 1487.
08-Mar-2021: Add objective for the sequence of par and seq elements in
media overlay documents to reflect a logical reading order. See issue 1556.
05-Mar-2021: Added recommendation that page markers be included for all pages of content
reproduced from source and best practice to include markers for all pages in the source. See issue 1502.
05-Mar-2021: Added recommendation that page list include links to all pages of content
reproduced from source and best practice to include links to all pages in the source. See issue 1503.
05-Mar-2021: Restructured the EPUB Requirements section to split out the individual objectives
that were grouped together under the Page Navigation and Media Overlays headings. See issue 1458.
25-Feb-2021: Replaced the IDPF URLs used to report conformance to the 1.0 specification with
more flexible text strings. See issue
1455.
19-Feb-2021: References to WCAG 2.0 have been updated to undated references to WCAG 2 (except
where WCAG 2.0 is explicitly mentioned for conformance).
01-Feb-2021: Changed the recommendation that media overlays conform to the requirements of the
EPUB specification to a requirement. See issue 1486.
17-Nov-2020: Added the refines attribute to the certifierCredential
and certifierReport properties and examples. See issue 1410.
16-Nov-2020: References to the optional accessibility control and API metadata have been removed
from the discoverability section. These metadata properties are more applicable to reading
systems. See issue 1327.
26-Sept-2020: The revisions made to the Accessibility 1.0 specification as part of publishing it
as an ISO standard have been incorporated into the initial draft text.
D. Acknowledgements
This section is non-normative.
The journey to make publications accessible for all can sometimes feels like a long and winding road. It
takes a special kind of person with strong dedication to the goal and an abundance of perseverance to
keep going even when it seems like there are still miles to go and many hills to climb. Ben Schroeter
was one such person, working tirelessly to help EPUB reach its potential as a universally accessible
format. We miss him greatly and dedicate this document to his memory.
The following members of the EPUB 3 Working Group contributed to the development of this specification:
Shadi Abou-Zahra (Amazon)
Will AWAD (Newgen Knowledgeworks)
Noel Ray Barron (Apple Inc.)
Sofia Bautista (Legible Media Inc.)
Leah Brochu (National Network for Equitable Library Service)
Matthew C. Chan (House of Anansi Press)
Yu-Wei Chang (Taiwan Digital Publishing Forum)
Juan Corona (Legible Media Inc.)
Dave Cramer (W3C Invited Expert, chair)
Romain Deltour (DAISY Consortium)
Marisa DeMeglio (DAISY Consortium)
Brady Duga (Google LLC)
Reinaldo Ferraz (NIC.br - Brazilian Network Information Center)
Symon Flaming (Rakuten Group, Inc.)
John Foliot (W3C Invited Expert)
Teenya Franklin (Pearson plc)
Hadrien Gardeur (EDRLab)
Matt Garrish (DAISY Consortium)
Jen Goulden (Crawford Technologies)
David Hall (Apple Inc.)
Ivan Herman (W3C, staff contact)
Tetsu Hoshino (Kodansha, Publishers, Ltd.)
jasen huang (ByteDance)
Norikazu Ishizu (Kadokawa Corporation)
Norihito IYENAGA (Kodansha, Publishers, Ltd.)
Rick Johnson (VitalSource Technologies)
Ken Jones (Circular Software)
Antonio Kamiya (Dentsu Group Inc.)
Deborah Kaplan (W3C Invited Expert)
Bill Kasdorf (Book Industry Study Group)
Hiroshi Kawada (MEDIA DO Co., Ltd.)
George Kerscher (DAISY Consortium)
Kazuhito Kidachi (Mitsue-Links Co., Ltd.)
Masakazu Kitahara (Voyager Japan, Inc.)
Toshiaki Koike (Voyager Japan, Inc.)
Ryo Kuroda (ACCESS CO., LTD.)
Charles LaPierre (Benetech)
Dan Lazin (Google LLC)
Philippe Le Hegaret (W3C)
Laurent Le Meur (EDRLab)
YuYu Lin (Taiwan Digital Publishing Forum)
Farrah Little (National Network for Equitable Library Service)
Victor Lopes (Apple Inc.)
Karan Malhotra (Newgen Knowledgeworks)
Makoto Murata (DAISY Consortium)
Cristina Mussinelli (Fondazione LIA)
Yoichiro Nagao (Kodansha, Publishers, Ltd.)
Theresa O'Connor (Apple Inc.)
Yoshinori Ohmura (SHUEISHA Inc.)
Rachel Osolen (National Network for Equitable Library Service)