EPUB Accessibility
Conformance and Discovery Requirements for EPUB Publications
Editor's Draft 26 April 2016
This version
http://www.idpf.org/epub/a11y/accessibility-20160426.html
Latest version
http://www.idpf.org/epub/latest/accessibility
Previous version
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Previous recommendation
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Document history
Errata
Editors
Matt Garrish (Invited Expert)
George Kerscher (DAISY Consortium)
Charles LaPierre (Benetech)
Avneesh Singh (DAISY Consortium)
Authors
Romain Deltour (DAISY Consortium)
Markus Gylling (International Digital Publishing Forum (IDPF))
Bernhard Heinser (Access for All)
Jean Kaplansky (Invited Expert)
Madeleine Rothberg (Invited Expert)
Tzviya Siegman (John Wiley & Sons)
Jason White (Invited Expert)
Copyright © 2016 International Digital Publishing Forum™
All rights reserved. This work is protected under Title 17 of the United States Code. Reproduction and dissemination of this work with changes is prohibited except with the written permission of the International Digital Publishing Forum (IDPF).
EPUB is a registered trademark of the International Digital Publishing Forum.
Status of this Document
This section describes the status of this document at the time of its publication. Other documents may supersede this document.
This document is a draft produced by the EPUB Working Group under the EPUB Working Group Charter approved on 8 July 2015.
This document is not considered stable and may be updated, replaced or obsoleted at any time. Its publication as a draft does not imply endorsement by IDPF membership or the IDPF Board. The document should only be cited as a work in progress.
Feedback on this document can be provided to the EPUB Working Group's mailing list (members only) or via the issue tracker (requires a GitHub account).
This document is governed by the IDPF Policies and Procedures.
Table of Contents
1.2 Application to Older Specifications
2.2 Reading System Conformance
2.3 Authoring Tool Conformance
4.2.1 WCAG Conformance Requirements
4.2.2 Evaluating WCAG Conformance
4.2.2.2 Applying the Conformance Criteria
4.3.2 Structured Audio Playback
4.3.4 Digital Rights Management
Acknowledgements and Contributors
This section is informative
This specification, EPUB Accessibility, addresses two key needs in the EPUB® ecosystem:
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 for consumers.
The inclusion of accessibility metadata facilitates informed decisions about the usability of an EPUB Publication. Consumers can review the qualities of the content and decide whether the EPUB Publication is appropriate for their needs, regardless of whether it meets the bar of being certified broadly accessible.
This specification does not target a single version of EPUB. It is designed to be applied 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.
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 reference to this one (e.g., EPUB 3.0.1 or EPUB 2.0.1).
Authors of such content are encouraged to create their publications in conformance with the accessibility requirements defined in this document even though it is not normatively required.
Assistive Technology
This specification adopts the meaning of an assistive technology from [WCAG20].
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.
Author
The person(s) or organization responsible for the creation of an EPUB Publication. The Author is not necessarily the creator of the content.
EPUB Authoring Tool
This specification adapts the meaning of authoring tool from [ATAG20]. An EPUB Authoring Tool differs only in that it is used to create or modify an EPUB Publication.
EPUB Content Document
A document that conforms to one of the EPUB Content Document definitions.
EPUB Publication
A collection of one or more Renditions that represents a single intellectual or artistic work. EPUB Publications are often, but not always, packaged as a single file.
Manifest Fallback
A mechanism in the Package Document manifest that allows Authors to identify alternative resources for those a Reading System might not support (i.e., to create fallback chains).
Optimization
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), but that doesn't meet the accessibility requirements of [WCAG20]. See 5. Optimized Publications.
Package Document
A resource that describes one Rendition of an EPUB Publication. The Package Document typically carries meta information, provides a manifest of resources and defines the default reading order.
Reading System
A system that processes EPUB Publications for presentation to a User.
Rendition
A logical document entity that represents one rendering of an EPUB Publication.
User
An individual that consumes an EPUB Publication using a Reading System.
NOTE
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
Links to markup and code definitions are underlined and in red monospace font.
http://www.idpf.org/
URIs are in navy blue monospace font.
hyperlink
Hyperlinks are underlined and in blue.
[reference]
Normative and informative references are enclosed in square brackets.
Term
Terms defined in the Terminology are in capital case.
Informative markup examples are in monospace font.
NOTE
Informative notes are preceded by a "Note" 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 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 appendices applies to all child content and subsections they may contain.
All examples in this specification are informative.
An EPUB Publication must include discovery metadata as defined in 3. Discovery.
An EPUB Publication must meet the following requirements to claim it is accessible per this specification:
If an EPUB Publication is an Optimization, it must be identified as defined in 5. Optimized Publications.
A conformant EPUB Reading System must meet the following requirements:
A conformant EPUB Authoring Tool must meet the following requirements:
This specification takes an abstract approach to the accessibility requirements for EPUB Publications, similar to how [WCAG20] separates its accessibility guidelines from the techniques to achieve them. This approach allows these guidelines to remain stable even as the format evolves.
To facilitate this approach, the companion EPUB Accessibility Techniques [A11YTech] document outlines conformance techniques. These techniques explain how to meet the requirements for different versions of EPUB.
Unlike Web pages, EPUB Publications are designed to be distributed through many channels for personal consumption – a model that has made EPUB a successful format for ebooks and other types of digital publications. One downside to this model, however, is that specific details about the accessibility of a publication typically do not follow 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 relay on to consumers what is present in the metadata.
Ensuring that the accessible qualities of an EPUB Publication can be discovered by any interested party is of paramount concern, as the suitability of an EPUB Publication can have real effects (e.g., the ability to use in educational settings). That the content meets the accessibility requirements of this specification is often not enough information, as any affordances made to meet the requirements are equally important to know when determining usability.
Similarly, content that does not meet the requirements of this specification is not necessarily inaccessible. Only through the inclusion of rich metadata can Users decide for themselves if the content is suitable for their needs.
Every conformant EPUB Publication must include metadata in the Package Document that describes its accessible properties, regardless of whether it meets the accessibility conformance requirements.
The following metadata is required:
It is additionally recommended to include the following metadata:
If the metadata allows the expression of other accessibility information, the inclusion of such metadata is also recommended, as appropriate.
If a metadata record is provided separately from the EPUB Publication (e.g., for ingestion into a vendor system), the record must include any corresponding accessibility metadata expressions the format allows.
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 to represent the content 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 [WCAG20]. This specification leverages the extensive work done in [WCAG20] to establish benchmarks for accessible content. 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 [WCAG20] and also addresses qualities unique to digital publications, such as page breaks and digital rights management.
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.
EPUB Publications must meet [WCAG20] Level A to be conformant with this specification, but it is recommended that they conform to Level AA.
NOTE
Local and national laws can influence the level of conformance an EPUB Publication has to meet, as can other EPUB specifications and even vendor procurement requirements. Any entity can demand content that exceeds the minimum requirements of this specification. If content has to conform by law to [WCAG20] Level AA, for example, that level has to be met. Compliance with this specification is not a shield against prosecution or penalty for failure to comply with such requirements.
The [WCAG20] Principles and Guidelines focus on the evaluation of individual Web pages, but an EPUB Publication more closely resembles what [WCAG20] 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 guidelines for content to be perceivable, operable, understandable and robust [WCAG20] 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 [A11YTech].
When evaluating an EPUB Publication, the [WCAG20] Conformance Criteria are applied as follow:
This specification does not require a [WCAG20] Conformance Claim, as conformance to this specification includes the WCAG conformance level attained (see 4.4 Conformance Reporting). Authors may include such a claim, however.
The requirements defined in this section are unique to EPUB Publications. As a result, an EPUB Publication can conform to [WCAG20] without conforming to this section, but any publication that does not meet the requirements of this section is not conformant to this specification.
NOTE
The IDPF plans to work with W3C and the Web Accessibility Initiative to formalize these requirements for digital publications.
Enable navigation of the content through the inclusion of structure and semantics in [SMIL]-based playback.
When an EPUB Publication contains SMIL-based text and audio synchronization, the structure and semantics of the content have to be paralleled in the SMIL markup to provide the same ease of navigation for auditory readers.
For example, if the SMIL markup contains only a single synchronization point for an entire table, the User will have to listen to all the data in sequence with no ability to navigate the rows or cells. The addition of equivalent structure to mimic the rows and cells in the markup allows the User to efficiently navigate the content, escaping from cells, rows or the entire table as he or she desires.
Similarly, including the semantics of the structures in the SMIL markup will allow a Reading System to offer the User the ability to skip past undesired content. When reading through a section, a User might prefer to only hear the primary content and automatically skip all sidebars, figures and other supplementary content. Without this information in the SMIL markup, such an enhanced reading experience is not possible.
If an EPUB Publication provides synchronized text and audio playback functionality, it should include the appropriate structure and semantics in the SMIL markup to skip and escape from content.
Provide navigation to static page break locations.
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 a feature of statically-paginated digital publications.
As a result, a non-visual reader in an environment where statically-paginated content is used is disadvantaged relative to his or her peers by not being able to locate the same spot.
The inclusion of print page boundaries helps bridge this disparity by ensuring that those using reflowable media are not disadvantaged by their choice.
NOTE
The pagination of reflowable content by Reading Systems is not static, since it typically changes depending on the viewport and font settings. Including page break markers in digital-only reflowable publications aids in navigation, as well, but currently there is no standard defined for their inclusion.
If a reflowable EPUB Publication represents a work that is also distributed in a statically paginated form, it should include a means of locating the static page break locations.
Ensure the application of digital rights management (DRM) does not impede access to the content of an EPUB Publication.
EPUB Publications typically require preservation of the publisher's and author's intellectual property when distributed (e.g., so that they can be made available for individual sale through online bookstores or distributed through library systems). The most common way to address this need has been through the application of DRM schemes to the packaged EPUB Publication. DRM enables a variety of security features that aren't native to the EPUB format, such as the ability to limit access to a single User and to limit the length of time the person can access the publication (e.g., library loans).
More problematic is that DRM schemes also provide the ability to remove access to the content. Such restrictions make it impossible to generate text-to-speech playback, for example, or for a refreshable braille display to access the text.
Digital rights management restrictions applied to EPUB Publications must not restrict access to the content in a way that impairs access by Assistive Technologies.
Open Issue #1
The metadata properties and values used to express conformance are still under consideration. The accessibility group was not able to find a single existing metadata vocabulary with properties needed to express this information. See issue #698 for more information.
To indicate an EPUB Publication conforms to all the requirements of this specification, it must include a [DCTERMS] conformsTo property report in its Package Document metadata.
The value of this property must be the IRI of the dated version of this specification the EPUB Publication conforms to followed by one of the following fragment identifiers:
The following example shows the URI for an EPUB Publication that
conforms to WCAG Level AA.
http://www.idpf.org/epub/a11y/accessibility-20160426.html#wcag-aa
An EPUB Publication that conforms to this specification also must include the name of the party that certified the content. This specification defines the following a11y:certifiedBy property for including this information.
Name: |
a11y:certifiedBy |
Namespace |
http://www.idpf.org/2016/accessibility |
Description: |
Identifies a party responsible for the testing and certification of the accessibility of an EPUB Publication. |
Applies to: |
EPUB Publication |
Cardinality: |
One or more |
Example |
<meta property="a11y:certifiedBy">Accessibility Testers Group</meta> |
The following example shows a complete conformance statement for an EPUB 3 Publication that meets the requirements of this specification to WCAG 2.0 Level A.
<package … prefix="a11y: http://www.idpf.org/2016/accessibility">
<metadata>
…
<meta property="dcterms:conformsTo">
http://www.idpf.org/epub/a11y/accessibility-20160426.html#wcag-a
</meta>
<meta property="a11y:certifiedBy">Acme Publishing Inc.</meta>
…
</metadata>
…
</package>
Although [WCAG20] 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 [WCAG20] because it is not designed for a broad audience. In these cases, failing to achieve a WCAG conformance level does not make the publications any less accessible to their intended audience.
To account for this discrepancy, this specification places importance on the inclusion of discovery metadata. An optimized EPUB Publication is discoverable to its intended audience through the inclusion of rich metadata, even if it is not identified as broadly accessible per this specification.
In addition to the metadata requirements defined in 3. 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.
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 a summary.
An optimized EPUB Publication must not claim accessibility conformance to this specification.
This specification does not define or recommend standards or guidelines for the production of content optimized.
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 was 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 this specification was undertaken by an accessibility subgroup led by:
Active members of the subgroup at the time of publication were:
IDPF Members
Invited Experts/Observers
[A11YTech] EPUB Accessibility Techniques.
[A11yTestSuite] EPUB Accessibility Tests.
[ATAG20] Authoring Tools Accessibility Guidelines (ATAG) 2.0. Jan Richards, et al. W3C Recommendation. 24 September 2015.
[DCTERMS] DCMI Metadata Terms.
[SMIL] SMIL Version 3.0. D. Bulterman, et al. 01 December 2008.
[RFC2119] Key words for use in RFCs to Indicate Requirement Levels (RFC 2119) . March 1997.
[RFC3987] Internationalized Resource Identifiers (IRIs) (RFC 3987). M Duerst, et al. January 2005.
[UAAG20] User Agent Accessibility Guidelines (UAAG) 2.0. James Allan, et al. W3C Working Group Note. 15 December 2015.
[WCAG20] Web Content Accessibility Guidelines (WCAG) 2.0. Ben Caldwell, et al. W3C Recommendation. 11 December 2008.