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Conformance and Discovery Requirements for EPUB Publications
Recommended Specification 5 January 2017
Copyright © 2010-2017 International Digital Publishing Forum™
All rights reserved. This work is protected under Title 17 of the United States Code. Reproduction and dissemination of this work with changes is prohibited except with the written permission of the International Digital Publishing Forum (IDPF).
EPUB is a registered trademark of the International Digital Publishing Forum.
This section is informative
This specification, EPUB Accessibility, addresses two key needs in the EPUB® ecosystem:
evaluation and certification of accessible EPUB Publications;
discovery of the accessible qualities of EPUB Publications.
Although it has always been possible to create EPUB Publications with a high degree of accessibility, this specification sets formal requirements to meet to certify content as accessible. These requirements provide Authors a clear set of guidelines to evaluate their content against, and allow certification of quality.
The inclusion of accessibility metadata, on the other hand, facilitates informed decisions about the usability of an EPUB Publication. Consumers can review the qualities of the content and decide whether an EPUB Publication is appropriate for their needs, regardless of whether it meets the bar of being certified broadly accessible.
This specification defines three categories of compliance for EPUB Publications:
Discoverable — an EPUB Publication that meets the discovery metadata requirements of this specification but does not meet the accessibility requirements. Conformance is defined in Discoverable EPUB Publications.
Accessible — an EPUB Publication that meets all discovery, [WCAG 2.0] and EPUB accessibility requirements. Conformance is defined in Accessible EPUB Publications.
Optimized — an EPUB Publication that meets the discovery requirements for Optimizations. Conformance is defined in Optimized EPUB Publications.
This specification does not target a single version of EPUB. It is designed to be applicable to EPUB Publications that conform to any version or profile, including future versions of the standard.
Ideally, these guidelines will be instructive in evaluating any digital publication built on Open Web technologies, although ensuring such application is outside the scope of this specification.
For additional background on the decisions that went into this specification, refer to the informative [Accessibility FAQ].
This specification takes an abstract approach to the accessibility requirements for EPUB Publications, similar to how [WCAG 2.0] separates its accessibility guidelines from the techniques to achieve them. This approach allows the guidelines to remain stable even as the format evolves.
To facilitate this approach, the companion [EPUB Accessibility Techniques] document outlines conformance techniques. The techniques explain how to meet the requirements of this specification for different versions of EPUB.
This section is informative
This specification is designed to be applicable to any EPUB Publication, even if the content conforms to an older specification that does not make reference to this one (i.e., specifications prior to [EPUB 3.1]).
Authors of such EPUB Publications are encouraged to create content in conformance with the accessibility requirements of this specification, even though it is not normatively required.
This specification adopts the meaning of an assistive technology from [WCAG 2.0].
Note that an assistive technology is not always a separate application from a Reading System. Reading Systems often integrate features of standalone assistive technologies, such as text-to-speech playback.
The person(s) or organization responsible for the creation of an EPUB Publication. The Author is not necessarily the creator of the content.
An EPUB Publication that includes a description of its accessible qualities in its Package Document metadata, as defined in Discovery.
Inclusion of this metadata allows users to make informed decisions about the usability of the EPUB Publication, even in cases where the content does not meet the accessibility requirements of this specification.
A system that provides users access to obtain EPUB Publications, such as an online bookstore or public library.
This specification adapts the meaning of authoring tool from [ATAG 2.0]. An EPUB Authoring Tool differs only in that it is has to be able to create or modify an EPUB Publication.
A document that conforms to one of the EPUB Content Document definitions.
A collection of one or more Renditions that represents a single intellectual or artistic work.
An EPUB Publication whose content is enhanced to be accessible by users with a specific need (e.g., dyslexia) or preferred reading modality (e.g., audio, tactile), so does not meet the broader accessibility requirements of [WCAG 2.0]. See Optimized Publications.
The Package Document describes one Rendition of an EPUB Publication. It carries meta information, provides a manifest of resources and defines the default reading order.
A system that processes EPUB Publications for presentation to a user.
A logical document entity that represents one rendering of an EPUB Publication.
Some terms have more precise meanings for a given version of EPUB. Refer to the appropriate specification for more information.
The following typographic conventions are used in this specification:
markup
All markup (elements, attributes, properties), code (JavaScript, pseudo-code), machine-readable values (string, characters, media types) and file names are in red monospace font.
markup link
Links to markup and code definitions are in underlined red monospace font.
http://www.idpf.org/
URIs are in navy blue monospace font.
Hyperlinks are underlined and blue.
Normative and informative references are enclosed in square brackets.
Terms defined in the Terminology are in capital case.
Links to term definitions have a dotted blue underline.
Normative element, attribute and property definitions are in blue boxes.
Informative markup examples are in light gray boxes.
Informative notes are in green boxes with a "Note" header.
Informative cautionary notes are in red boxes with a "Caution" header.
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL in this document are to be interpreted as described in [RFC2119].
All sections and appendixes of this specification are normative except where identified by the informative status label "This section is informative". The application of informative status to sections and appendixes applies to all child content and subsections they contain.
All examples in this specification are informative.
A Discoverable EPUB Publication must meet the following criteria:
It must include discovery metadata as defined in Discovery.
An EPUB Publication must meet the following criteria to be accessible per this specification:
It must meet the requirements for Discoverable EPUB Publications.
It must meet the requirements for [WCAG 2.0] conformance defined in WCAG Conformance Requirements.
It must meet the requirements for EPUB Publications defined in EPUB Requirements.
It must include accessibility conformance metadata as defined in Conformance Reporting.
An Optimized EPUB Publication must meet the following criteria:
It must meet the requirements for Discoverable EPUB Publications.
It must identify the standard or guidelines it conforms to as defined in Optimized Publications.
Regardless of the type or level of accessibility an EPUB Publication achieves, it must be distributed accessibly, as defined in Distribution.
This section is informative
Unlike Web pages, EPUB Publications are designed to be distributed through many channels for personal consumption — a model that has made EPUB a successful format for ebooks and other types of digital publications. A consequence of this model, however, is that specific details about the accessibility of a publication need to travel with it.
An online bookstore aggregating content from publishers and authors, for example, does not know the production quality that went into each submission, so can only convey to consumers what is present in each publication's metadata.
Ensuring that the accessible qualities of an EPUB Publication can be discovered by any interested party is therefore a primary concern. Users need to be able to gauge the usability of an EPUB Publication when they purchase, borrow or otherwise obtain it, a determination that requires knowing the any affordances made to meet the accessibility requirements.
Similarly, content that does not meet the requirements of this specification, while not broadly accessible, might still meet the needs of individual users. Only through the inclusion of rich metadata can a user decide if the content is suitable for them.
Every conformant EPUB Publication must include the following [schema.org] 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).
accessibilitySummary — a human-readable summary of the overall accessibility, which includes a description of any known deficiencies (e.g., lack of extended descriptions, specific hazards).
Inclusion of the following [schema.org] accessibility metadata is recommended:
accessModeSufficient — a set of one or more access modes sufficient to consume the content without significant loss of information. An EPUB Publication might have more than one set of sufficient access modes for its consumption depending on the types of content it includes (i.e., unlike accessMode, this property takes into account any affordances for content that is not broadly accessible, such as the inclusion of transcripts for audio content).
Inclusion of the following [schema.org] accessibility metadata is optional:
accessibilityAPI — indicates the resource is compatible with the specified accessibility API. This property is typically only used to indicate that the use of scripting in an EPUB Publication follows [WAI-ARIA 1.1] authoring practices, as compatibility with operating system accessibility APIs is a concern for Reading Systems.
accessibilityControl — identifies input methods that can be used to access the content (e.g., keyboard, mouse).
See Discovery Metadata Techniques [EPUB Accessibility Techniques] for more information on these properties and how to include them in different versions of EPUB.
See also DIST-002: Include accessibility metadata in distribution records [EPUB Accessibility Techniques] for more information on including accessibility metadata in other formats.
The above recommendations cover all [schema.org] accessibility properties at the time of publication. If new properties are added in the future, Authors are encouraged to include them, as applicable, until such time as this specification can be updated.
Inclusion of accessibility metadata from other vocabularies is optional.
Accessibility metadata can also be included in linked records [Packages], but the inclusion of such metadata solely in a linked record does not satisfy the discovery requirements of this specification.
The precedence given to linked records varies depending on the version of EPUB (linked records have higher precedence than the package metadata in [EPUB 3.1], but lower precedence in earlier versions). As a result, Authors need to take care to ensure that accessibility metadata in the Package Document and any linked records do not contain contradictory statements, as it can affect the information a Reading System presents to the user.
This section is informative
EPUB is built on the Open Web Platform, with HTML, CSS, JavaScript and SVG the core technologies used for content authoring. The use of these technologies means that EPUB Publications can be authored with a high degree of accessibility simply through the proper application of established Web accessibility techniques.
The primary source for the production of accessible Web content is the W3C Web Content Accessibility Guidelines (WCAG) 2.0 [WCAG 2.0]. This specification leverages the extensive work done in [WCAG 2.0] to establish benchmarks for accessible content, and the same four high-level content principles — Perceivable, Operable, Understandable and Robust — are central to creating accessible EPUB Publications.
This section defines how to apply the conformance criteria defined in [WCAG 2.0] and also addresses qualities unique to EPUB Publications.
EPUB Publications authored to comply with the requirements in this section will have a high degree of accessibility for users with a wide variety of reading needs and preferences.
This section is informative
[WCAG 2.0] and [WCAG 2.0 Techniques] provide extensive coverage of issues and solutions for Web content accessibility — from tables to embedded multimedia to rich semantics. They represent the foundation that this specification builds upon.
This specification does not repeat the requirements or techniques introduced in those documents, as it risks breaking compatibility between the two standards (e.g., putting guidance out of sync, or in conflict). At the same time, although the requirements are not individually called out, it does not diminish their importance in creating accessible EPUB Publications.
This specification instead adds an additional set of requirements for EPUB Publications. These requirements are no more or less important than those covered in WCAG; they are simply necessary to follow for EPUB Publications. (The relationship to WCAG is explained for each requirement in its respective section.)
The same is true of the techniques in the [EPUB Accessibility Techniques] document. It provides coverage of techniques that are unique to EPUB Publications, or that need clarification in the context of an EPUB Publication. It does not mean that the rest of the WCAG techniques are not applicable.
As a result, although this section can be read without deep knowledge of WCAG conformance, to implement the accessibility requirements of this specification will require an understanding of [WCAG 2.0].
Because this specification adds requirements that are not a part of WCAG, an EPUB Publication can conform to [WCAG 2.0] without conforming to this specification. An EPUB Publication that does not meet the requirements for EPUB Publications is not accessible to this specification, however.
The IDPF plans to work with W3C and the Web Accessibility Initiative to harmonize the requirements for EPUB Publications with WCAG.
EPUB Publications must meet [WCAG 2.0] Level A to be conformant with this specification, but it is recommended that they meet Level AA.
Although this specification only requires Level A conformance, local and national laws can influence the level of conformance an EPUB Publication has to meet to be considered accessible. Level AA conformance is often cited as the benchmark for accessibility in legal frameworks and policies, for example. Additionally, any procurer or distributor of EPUB Publications can demand higher conformance requirements than the baseline defined here.
Authors consequently need to ensure they understand the requirements their content has to meet to be considered accessible in any jurisdiction or distribution context, including seeking any necessary legal advice. Minimum conformance with this specification does not supersede such requirements, and does not offer protection from any legal liability that might arise.
The [WCAG 2.0] Principles focus on the evaluation of individual Web pages, but an EPUB Publication more closely resembles what [WCAG 2.0] refers to as a set of Web pages: "[a] collection of Web pages that share a common purpose".
Consequently, when evaluating the accessibility of an EPUB Publication, individual pages — or Content Documents, as they are known in EPUB nomenclature — cannot be reviewed in isolation. Rather, their overall accessibility as parts of a larger work also has to be evaluated.
For example, it is not sufficient for individual Content Documents to have a logical reading order if the publication presents them in the wrong order. Likewise, including a title for every Content Document is complementary to providing a title for the publication: the overall accessibility is affected if either is missing.
The [WCAG 2.0] guidelines for content to be perceivable, operable, understandable and robust therefore must be evaluated against the full EPUB Publication, not only to each Content Document within it.
More information about applying these guidelines to EPUB Publications is available in the [EPUB Accessibility Techniques].
When evaluating an EPUB Publication, the [WCAG 2.0] Conformance Criteria are applied as follows:
When determining compliance with a Conformance Level, the EPUB Publication as a whole must meet the conformance requirements of the level claimed.
Authors
must not use EPUB's fallback mechanisms to provide a conforming alternate version [WCAG 2.0], as there is no reliable way for users to
access such fallbacks. If fallbacks are used, both the primary content and its
fallback(s) must meet the requirements for the
conformance level claimed. EPUB-specific fallback mechanisms include manifest
fallbacks, bindings and content switching via the epub:switch element.
When determining compliance with the "Full Pages" requirement (i.e., that parts of a page cannot be excluded when making a conformance claim), the entirety of each content document must achieve the conformance level and every content document in the publication must meet the stated conformance level.
This section is informative
Structure Media Overlays to provide more accessible playback experiences.
Media Overlays provide an accessible playback experience for anyone who benefits from having text and audio synchronized. They are also useful to users who only require audio playback, or only benefit from reading with text highlighting. Media Overlays also enable a seamless playback experience from beginning to end of an EPUB Publication for all these users.
The most basic Media Overlay Documents [Media Overlays] provide only minimal instructions to Reading Systems, however. They indicate the text to highlight and the audio clip that corresponds to the text. The result is that users only have basic start and stop options available.
Authors need to add structure and semantics to Media Overlay Documents to allow Reading Systems to present more usable experiences. With richer markup, a Reading System could provide the ability to skip past secondary content that interferes with the primary narrative, escape users from deeply nested structures like tables, and allow them to navigate through the sections of the publication without having to go to the table of contents.
Media Overlay Documents do not have to meet any additional requirements beyond those defined in [Media Overlays] to be conformant with this specification.
To improve the usability of Media Overlays, however, Authors are encouraged to ensure their EPUB Publications meet the following criteria:
Identify all skippable structures [Media Overlays] in the Media Overlay Documents.
Identify all escapable structures [Media Overlays] in the Media Overlay Documents.
A future version of this specification might introduce stricter conformance requirements for Media Overlay Documents.
Adding structure and semantics to Media Overlay Documents broadly falls under the objective of the [WCAG 2.0] Info and Relationships success criterion. Without structured and semantically meaningful playback sequences, the effect is to deprive users rich navigation of the content.
To indicate that an EPUB Publication conforms to the accessibility requirements of this specification, it must include a conformsTo property [DCTERMS] and an a11y:certifiedBy property [Accessibility Vocab].
The value of the conformsTo property must be one of the following IRIs:
http://www.idpf.org/epub/a11y/accessibility-20170105.html#wcag-a
The EPUB Publication meets all accessibility requirements and achieves [WCAG 2.0] Level A conformance.
http://www.idpf.org/epub/a11y/accessibility-20170105.html#wcag-aa
The EPUB Publication meets all accessibility requirements and achieves [WCAG 2.0] Level AA conformance.
http://www.idpf.org/epub/a11y/accessibility-20170105.html#wcag-aaa
The EPUB Publication meets all accessibility requirements and achieves [WCAG 2.0] Level AAA conformance.
The a11y:certifiedBy property specifies the name of the party that certified the content. The certifier of the content could be the same party that created the EPUB Publication, but can also be a third party accessibility certifier.
The following example shows an EPUB 3 Publication that has been self-certified by the publisher (the
values of the dc:publisher and a11y:certifiedBy property are the same).
<metadata> … <dc:publisher>Acme Publishing Inc.</dc:publisher> <meta property="a11y:certifiedBy">Acme Publishing Inc.</meta> <link rel="dcterms:conformsTo" href="?x=http://www.idpf.org/epub/a11y/accessibility-20170105.html#wcag-aa"/> … </metadata>
The following example shows an EPUB 3 Publication that has been certified by a third party (the values
of the dc:publisher and a11y:certifiedBy
property differ).
<metadata> … <dc:publisher>Acme Publishing Inc.</dc:publisher> <meta property="a11y:certifiedBy">Foo's Accessibility Testing</meta> <link rel="dcterms:conformsTo" href="?x=http://www.idpf.org/epub/a11y/accessibility-20170105.html#wcag-aa"/> … </metadata>
The following example shows an EPUB 3 Publication that has been self-certified by the author.
<metadata> … <dc:creator>Jane Doe</dc:creator> <meta property="a11y:certifiedBy">Jane Doe</meta> <link rel="dcterms:conformsTo" href="?x=http://www.idpf.org/epub/a11y/accessibility-20170105.html#wcag-aa"/> … </metadata>
The following example shows a self-certified EPUB 2 Publication.
<metadata> … <dc:publisher>Acme Publishing Inc.</dc:publisher> <meta name="dcterms:conformsTo" content="http://www.idpf.org/epub/a11y/accessibility-20170105.html#wcag-aa"/> <meta name="a11y:certifiedBy" content="Acme Publishing Inc."/> … </metadata>
If an EPUB Publication is certified by an organization, users will typically want to know the name of that organization. Including the name of the individual(s) who carried out the assessment, instead of the name of the certifying organization, is generally discouraged, as it can diminish the trust the user has in the claim.
If the party that certifies the content has been issued a credential or badge that establishes their authority to certify content accessible, that information can be supplied in an a11y:certifierCredential property [Accessibility Vocab].
The following example shows a credential.
<meta property="a11y:certifierCredential">A+ Accessibility Rating</meta>
If the party that certifies the content has provided a detailed report of its assessment, a link to the assessment can be provided in an a11y:certifierReport property [Accessibility Vocab].
The following example shows a link to a remotely-hosted accessibility report.
<link rel="a11y:certifierReport"
href="?x=http://www.example.com/a11y/report/9780000000001"/>
The following example shows a link to a locally-hosted accessibility report.
<link rel="a11y:certifierReport" href="?x=http://idpf.orgreports/a11y.xhtml"/>
As each metadata format is unique in what it can express, this specification does not mandate how conformance metadata is expressed outside of the Package Document.
This specification does not define a conformance level for EPUB Publications that only meet the discovery metadata requirements, as the usability of such content by any given user can only be determined from the accessibility metadata. Reporting requirements for Optimized Publications are defined in the next section.
Although [WCAG 2.0] provides a general set of guidelines for making content broadly accessible, conformant content is not always optimal for specific user groups. Conversely, content optimized for a specific need or reading modality is often not conformant to [WCAG 2.0] because it is not designed for a broad audience.
For example, an EPUB Publication with synchronized text and audio might contain a full audio recording of the content but limit the text content to only the major headings. In this case, the EPUB Publication is consumable by users who needs to hear the content (i.e., they can listen to the full publication and can navigate between headings), but it is not usable by anyone who cannot hear the audio.
In other words, when an EPUB Publication is optimized for specific reading modalities, the failure to achieve a WCAG conformance level does not make it any less accessible to the intended audience.
To account for this discrepancy, this specification places importance on the inclusion of discovery metadata. An Optimized EPUB Publication is discoverable to its intended audience through the inclusion of rich metadata, even if it is not identified as broadly accessible per this specification.
In addition to the metadata requirements defined in Discovery, an optimized EPUB Publication must identify the standard or guidelines the content adheres to in a [DCTERMS] conformsTo property. The value of this property must be an IRI [RFC3987] that references the standard or guidelines it follows.
The following example shows a conformance statement for an EPUB 3 Publication that conforms to the [DAISY Audio] guidelines.
<package …>
<metadata>
…
<link rel="dcterms:conformsTo" href="?x=http://www.daisy.org/guidelines/epub/navigable-audio-only-epub3-guidelines"/>
…
</metadata>
…
</package>
If the IRI is not sufficient for a user to understand conformance (e.g., the guidelines are not publicly available), more information about how the content has been optimized should be provided in the accessibility summary.
The following example shows an accessibility summary for an EPUB Publication optimized for braille rendering.
<meta property="schema:accessibilitySummary">
This publication is optimized for braille readers. It will not be
usable by persons who cannot read braille. The publication is designed
for braille reading devices capable of displaying 6 character cells and
40 character line lengths. The text is not contracted, and follows
Unified English Braille formatting conventions. All characters are
encoded using the Unicode braille character set.
</meta>
The following example shows an accessibility summary for an EPUB Publication optimized for audio rendering.
<meta property="schema:accessibilitySummary">
This publication is an audio book. It will not be usable by persons who
cannot hear the audio. The publication is recorded by a professional
narrator. There is navigation to the beginning of each chapter. The text
of the publication is not included. Images are not included, but the
photo captions are narrated at the end of the chapter where they occur.
</meta>
This specification does not define or recommend standards or guidelines for the production of optimized content. An informative registry of optimization standards is maintained separately from this specification, but no endorsement of them is implied.
The creation of an accessible EPUB Publication does not in itself guarantee that the content will be obtainable or consumable by users. Depending on the Distribution System used, other factors will influence the overall accessibility of the EPUB Publication.
This specification distinguishes factors that an Author has influence over from those that they do not. For example, an accessible interface for locating and obtaining content is an essential part of the distribution process, as is the ability to search and review accessibility metadata. Such interfaces are typically out of the control of content Authors, however, as distribution of EPUB Publications is often done through third parties. But even when Authors control their Distribution Channel, the accessibility of these applications is outside the scope of this specification, as such considerations are not appplicable to the EPUB Publications themselves.
At the same time, there are decisions Authors have to make when their content is ingested into Distribution Systems, such as what digital rights to apply. Although these decisions are not part of the preparation of the content, their potential impact on users requires special attention.
To minimize the effects of distribution on accessibility, Authors therefore must adhere to the following distribution practices:
if digital rights management protection is applied to an EPUB Publication, the Author must not impose restrictions that impair access by Assistive Technologies.
if a distributor requires that a distribution record (e.g., ONIX) accompany an EPUB Publication, the Author must include any accessibility metadata in the record that the format allows.
For more information about the accessibility of Distribution Systems, refer to Distribution System Conformance.
Although this specification focuses on content requirements for accessible EPUB Publications, there are two additional considerations in making EPUB Publications available to everyone: the ability for anyone to be able to create an EPUB Publication and the ability for anyone to consume the content.
Although these needs are not the primary focus of this specification, this appendix provides conformance requirements for the creation of accessible Authoring Tools, Distribution Systems and Reading Systems. Developers who meet or exceed these requirements will make their applications usable by a wide variety of users.
This appendix could be superseded by specifications dedicated to these concerns in the future.
A conformant EPUB Authoring Tool must meet the following criteria:
It must meet the requirements for [ATAG 2.0] Level A conformance, with the following clarifications for Part B:
It must include support for the EPUB-specific requirements defined in EPUB Requirements where [ATAG 2.0] references the generation of accessible web content (as applicable to the content it can generate).
It must support [WCAG 2.0] accessibility requirements as they relate to EPUB Publications, including support for adding discovery metadata as defined in Package Metadata. See Page and Publication for more information.
It should meet the requirements for [ATAG 2.0] Level AA conformance, with the same clarifications defined in the preceding criterion.
A conformant Distribution System must meet the following criteria:
Its user interface must conform to [WCAG 2.0] Level AA.
It must provide the ability to narrow search results by the available accessibility metadata.
A conformant Reading System must meet the following criteria:
It must pass all the [A11Y Test Suite] Fundamental Accessible Reading System Tests.
It should meet the requirements for [UAAG 2.0] Level AA conformance.
This section is informative
EPUB has been developed by the International Digital Publishing Forum in a cooperative effort, bringing together publishers, vendors, software developers, and experts in the relevant standards.
The EPUB Accessibility specification and techniques were prepared by the International Digital Publishing Forum’s EPUB Maintenance Working Group, operating under a charter approved by the membership in July 2015, under the leadership of:
Work on these documents was undertaken by an accessibility subgroup led by:
Active members of the working group included:
For more detailed acknowledgements and information about contributors to each version of EPUB, refer to Acknowledgements and Contributors [EPUB3 Overview].
[A11Y Test Suite] EPUB Accessibility Tests .
[ATAG 2.0] Authoring Tools Accessibility Guidelines (ATAG) 2.0 .
[Accessibility Vocab] EPUB Accessibility Vocabulary .
[DCTERMS] DCMI Metadata Terms .
[EPUB 3.1] EPUB 3.1 .
[Media Overlays] EPUB Media Overlays 3.1 .
[Packages] EPUB Packages 3 .
[RFC2119] Key words for use in RFCs to Indicate Requirement Levels (RFC 2119) . March 1997.
[RFC3987] Internationalized Resource Identifiers (IRIs) (RFC 3987) . January 2005.
[UAAG 2.0] User Agent Accessibility Guidelines 2.0 . 17 December 2002.
[WAI-ARIA 1.1] Accessible Rich Internet Applications (WAI-ARIA) 1.1 .
[WCAG 2.0] Web Content Accessibility Guidelines (WCAG) 2.0 .
[WCAG 2.0 Techniques] Techniques for WCAG 2.0. .
[schema.org] schema.org.
[Accessibility FAQ] EPUB Accessibility Frequently Asked Questions.
[DAISY Audio] Navigable audio-only EPUB 3 Guidelines .
[EPUB Accessibility Techniques] EPUB Accessibility Techniques .
[EPUB3 Overview] EPUB 3.1 Overview .