EPUB Accessibility Techniques defines discovery and content accessibility requirements for EPUB® Publications.

Overview

Purpose and scope

This document, EPUB Accessibility Techniques, provides guidance on how to meet the [[epub-a11y-11]] discovery and accessibility requirements for EPUB publications.

This document does not cover techniques and best practices already addressed in [[wcag2]] and [[wai-aria]] for which no substantive differences in application exist.

Terminology

This document uses terminology defined in EPUB 3.3 [[epub-3]] and EPUB Accessibility 1.1 [[epub-a11y-11]]:

Only the first instance of a term in a section links to its definition.

About the techniques

The accessibility techniques described in this document are advisory in nature. They are intended to help EPUB creators create EPUB publications that conform to the requirements in [[epub-a11y-11]], but they are not all applicable in all situations and there may be other ways to meet the requirements of that specification. As a result, this document should not be read as providing prescriptive requirements.

These techniques also do not address issues in digital publishing for which no universally accessible solutions exist. The W3C's Digital Publishing Interest Group has published a note that outlines many of these issues [[dpub-accessibility]]. As solutions become available, they will be incorporated into the appropriate document, whether this one or one it refers to.

If EPUB creators encounter issues that are not covered in these or related techniques, they are encouraged to report the issue to the appropriate community for guidance on how to meet accessibility standards. The W3C Web Accessibility Interest Group has a public mailing list where issues meeting [[wcag2]] and [[wai-aria]] requirements can be raised. The W3C Publishing Community Group issue tracker can be used to ask for support implementing EPUB-specific requirements and the EPUB 3 Working Group's issue tracker to report issues with this document.

Discovery metadata techniques

Identify primary access modes

An access mode is defined as a "human sense perceptual system or cognitive faculty through which a user may process or perceive the content of a digital resource." [[iso24751-3]] For example, if an EPUB publication contains images and video, visual perception is required to consume the content exactly as it was created.

There are four access modes that are typically specified for EPUB publications:

For a user to determine whether an EPUB publication is suitable for their needs, they need to know which of these access modes are required to consume the content. List all applicable access modes in the [[schema-org]] accessMode property, repeating the property for each applicable mode.

Note that the access modes of the content do not reflect any adaptations that have been provided. For example, if a comic book also includes alternative text for each image, it does not have a textual access mode. See the following section on sufficient access modes for how to indicate that the available adaptations allow the content to be consumed in another mode.

Refer to The accessMode Property [[a11y-discov-vocab]] for more information about this property and its values.

Identify sufficient access modes

The access modes sufficient to consume an EPUB publication express a broader picture of the potential usability than do the basic access modes. Where the basic access modes identify the default nature of the media used in the publication, sufficient access modes identify which modes, or sets of modes, a user requires to read the publication. Sufficient access modes account for the affordances and adaptations that have been provided, allowing a user to determine whether the content will be usable regardless of its default nature.

Sufficient access modes are identified in the [[schema-org]] accessModeSufficient property. Repeat the property for each set of sufficient access modes.

For example, consider an EPUB publication that contains graphics and charts, as well as descriptions for all these images. The publication has both textual and visual content, so the EPUB creator will include the following metadata entries to indicate this:

<meta
    property="schema:accessMode">
   textual
</meta>
<meta
    property="schema:accessMode">
   visual
</meta>

This metadata does not make clear whether a textual access mode is sufficient to read the entire publication, or whether a visual one is, only that two modes are required by default. This discrepancy is why sufficiency is also important to know.

The first set of sufficiency metadata the EPUB creator inputs will establish the textual and visual requirement:

<meta
    property="schema:accessModeSufficient">
   textual,visual
</meta>

The order in which the access modes are listed is not important. The only requirement is that they be separated by commas.

Since the EPUB creator has also included descriptions for all the images, the EPUB creator can also indicate that a purely textual access mode is sufficient to read the content:

<meta
    property="schema:accessModeSufficient">
   textual
</meta>

Without this metadata, users would not have known that they could read the publication only via its text content.

A sufficient access mode of "visual" is not provided as the content is not entirely image-based. Textual content is considered a separate mode as it can be read both visually and aurally (text-to-speech). Photo books without text would be examples of works with a purely visual sufficient access mode.

The full set of entries in this example is as follows:

<meta
    property="schema:accessMode">
   textual
</meta>
<meta
    property="schema:accessMode">
   visual
</meta>
<meta
    property="schema:accessModeSufficient">
   textual,visual
</meta>
<meta
    property="schema:accessModeSufficient">
   textual
</meta>

Note that sufficiency of access is often a subjective determination of the EPUB creator based on their understanding of what information is essential to comprehending the text. Some information loss occurs by not being able to view a video, for example, but the EPUB creator might regard the visual or auditory losses as inconsequential if a transcript provides all the necessary information to understand the concepts being conveyed.

Refer to The accessModeSufficient Property [[a11y-discov-vocab]] for more information about this property and its values.

The accessModeSufficient property, as defined in [[schema-org]], allows more complicated expressions than can be represented in the EPUB 2 or 3 package document (e.g., definition of lists of values and inclusion of a human-readable description). A future version of EPUB might allow for richer metadata, but the basic expression shown in this section is sufficient for discovery purposes.

Identify accessibility features

Identifying all the accessibility features and adaptations included in an EPUB publication allows users to determine whether the content is usable at a more fine-grained level than the access modes do.

For example, a math textbook might have a textual access mode, but that alone does not indicate whether MathML markup is available. Whether a visual work only provides alternative text or whether it includes extended descriptions is also important to know when gauging its usability.

Accessibility features are identified in the [[schema-org]] accessibilityFeature property. Repeat this property for each feature.

The EPUB format requires that some accessibility features will always be present (e.g., a table of contents). Do not exclude these features from the accessibility metadata, as users typically are not aware what features are built into a format. Failing to include entries will reduce the discoverability of the publication when users search for specific features.

Refer to The accessibilityFeature Property [[a11y-discov-vocab]] for more information about this property and its values.

Identify accessibility hazards

There are three widely recognized hazards that can affect readers of digital content:

EPUB creators have to report whether their EPUB publications contain resources that present any of these hazards to users, as they can have real physical effects.

What precisely constitutes a sound hazard, and how to test for these hazards, is not standardized as of publication of this document. EPUB creators will have to use their discretion on when to specify a sound hazard until additional guidance is developed. This technique will be updated whenever there is more clarity on this issue.

Hazards are identified in the [[schema-org]] accessibilityHazard property. Repeat this property for each hazard.

Unlike other accessibility properties, the presence of hazards can be expressed both positively and negatively. This design decision was made because users most often search for content that is free from hazards that affect them, but also want to know what dangers are present in any publications they discover.

Do not skip reporting hazards just because an EPUB publication does not contain any content that could present risks. Users cannot infer a meaning when no metadata is present. The value "none" can be used in such cases instead of repeating each non-hazard.

If an EPUB publication contains a hazard, provide additional information about its source and nature in the accessibility summary.

If hazards cannot be definitively determined, report the value "unknown".

Refer to The accessibilityHazard Property [[a11y-discov-vocab]] for more information about this property and its values.

Include an accessibility summary

An accessibility summary provides a brief, human-readable description of the accessibility characteristics of an EPUB publication, or lack thereof.

If an EPUB publication does not meet the requirements for content accessibility in [[epub-a11y-11]], the reason(s) it fails should be noted in the summary.

An accessibility summary is provided using the [[schema-org]] accessibilitySummary property.

Do not repeat this property unless it contains the summary in another language. In the case of multiple summaries, use the xml:lang attribute to differentiate the language.

Refer to The accessibilitySummary Property [[a11y-discov-vocab]] for more information about this property.

Identify ARIA conformance

The use of the schema:accesibilityAPI property is no longer necessary for EPUB publications. EPUB creators are not responsible for the interaction between reading systems and the underlying platform APIs.

Meeting the requirements of [[wcag2]] is a better measure of the accessibility of scripting, as this property does not differentiate between ARIA markup used for document structure or for identifying controls.

Identify input control methods

The use of the schema:accesibilityControl property is no longer necessary for EPUB publications. This property does not differentiate issues arising from the reading system interface from those in the underlying content, which has led to confusion about its use.

Meeting the requirements of [[wcag2]] will mitigate most known issues with the content and is sufficient for authoring purposes.

Examples

The following examples show the metadata that would be added to an EPUB publication that has textual and visual access modes, is sufficient for reading by text, contains alternative text and MathML markup, and has a flashing hazard.

WCAG techniques

General guidance

Techniques for meeting the requirements of the [[wcag2]] are defined in Techniques for WCAG. This document does not repeat those techniques.

In general, the differences between the application of WCAG techniques to web pages and their application to EPUB content documents is minimal, but the following sections outline some key differences.

One point to note is that the WCAG techniques cover a greater range of technologies and content types than are typically found in an EPUB publication, so many are not applicable.

The following sets of techniques are the most applicable to EPUB content documents:

Other techniques will apply depending on the technologies used (e.g., a [[swf]] video in EPUB 2) or any alternative formats embedded in the EPUB publication (e.g., a PDF form).

Helpful resources

EPUB creators not familiar with the [[wcag2]] may find the number of techniques daunting, as they are intended to provide broad coverage of possible solutions.

Assistance applying these techniques to EPUB content documents is available from the following sources:

Content access

Ensure meaningful order of content across spreads

[[wcag2]] Success Criterion 1.3.2 specifies that each web page have a meaningful order (i.e., that the visual presentation of the content match the underlying markup).

As EPUB allows two EPUB content documents to be rendered together in a synthetic spread [[epub-3]], the order of content within a single document cannot always be evaluated in isolation. Content may span visually from one document to the next. For example, a sidebar might span the bottom of two pages.

Ordering each document separately by the visual display will lead to users of assistive technologies encountering gaps between the start and end of the spanned text. If the markup cannot be arranged to provide a more logical reading experience (e.g., the beginning of the spanned content at the end of the first page followed by the conclusion at the start of the next), another means of satisfying this criteria will be necessary to avoid failure (e.g., a hyperlink could be provided to allow a user to jump from the break point on the first page to the continuation on the next).

Provide multiple ways to access the content

[[wcag2]] Success Criterion 2.4.5 requires there be more than one way to locate a web page within a set of web pages. By default, EPUB publications meet this WCAG requirement so long as EPUB creators follow the EPUB requirements to include all EPUB content documents in the spine and ensure access to all non-linear documents [[epub-3]].

The reason an EPUB publication passes by meeting these requirements has to do with differences in how a user interacts with the set of documents in an EPUB publication. In particular, although an EPUB publication typically consists of many EPUB content documents, reading systems automatically provide the ability for the user to move seamlessly from one document to the next, so long as they are listed in the spine [[epub-3]]. To the user, an EPUB publication is a single document they have complete access to, not a set of disconnected pages that they need links to move through.

The required table of contents provides a second method to access the major headings of the publication. The user can jump to any heading and continue to navigate from there, regardless of how the publication is chunked.

Following these two requirements therefore satisfies the need for multiple ways to access the content. Reading systems also typically provide search capabilities, something the EPUB creator cannot provide, so users also have a third option available in most cases.

Although EPUB creators only need to follow EPUB requirements to meet this criterion, they are still encouraged to provide additional methods to improve access beyond the minimum. Some suggestions include:

  • adding at least one link to every EPUB content document in the spine to the table of contents, when feasible;

  • adding an index to locate major topics; and

  • adding additional navigation aids to the EPUB navigation document (e.g., lists of figures and tables).

Note about the table of contents

A common question about the EPUB table of contents is what completeness it needs to have with respect to the headings of the publication. Although the obvious answer seems like it should be a simple aggregation of all headings for all sections, practically there are several usability challenges to this approach.

Factors such as device screen sizes can make the table of contents for publications with a deep hierarchy of headings unreadable, so EPUB creators will trim headings below a certain depth to improve the readability. Further, reading systems do not always provide structured access to the headings in the table of contents, or provide shortcuts to navigate the links. The result is that users have to listen to each link one at a time to find where they want to go, a tedious and time-consuming process.

Although it is expected that reading systems will improve access to the table of contents as accessibility support for EPUB evolves — making complete tables of contents usable by everyone — there are legitimate usability reasons why they are not provided now.

When EPUB creators choose not to provide links to all the headings, however, they should optimize the linking they do provide for the best overall reading experience. Some considerations on how to achieve this include:

  • ensuring that there is at least one link to every EPUB content document — allowing the user to reach each document simplifies navigation to the minor headings within them; and

  • only omitting minor headings from the table of contents — although a subjective decision, there is often a level of diminishing value for navigation (e.g., fourth level and lower headings often only delimit short subsections on a topic).

Ensure the order of table of contents entries matches linear order

The table of contents provides users more than just links into the content. It is also a means to understand the structure and ordering of an EPUB publication. Consequently, users may have difficulty locating where they are in a publication, where they want to go, and also how to return to previous locations when the order of entries in the table of contents does not match the linear reading order.

EPUB creators should therefore ensure that the entries in the table of contents always match the linear order of the content. Specifically, the order of entries should reflect both:

  • the order of EPUB content documents in the spine; and
  • the order of each referenced section within its respective EPUB content document.

Only if there is a logical case for an alternative arrangement of entries should the ordering differ. Such scenarios typically only occur when the content does not have to be read linearly or when additional information is included at the end of a table of contents. For example, the table of contents for a magazine might be ordered to list all the major articles first, followed by features, etc.

When the ordering of the table of contents does not match the content, EPUB creators should include an explanation why in the accessibility summary.

EPUB creators should avoid including links to supplementary content at the end of the table of contents. Links to figure, tables, illustrations and similar content is better included as a separate navigation elements (either in the EPUB navigation document or in the spine). EPUB creators can include links to these additional navigation lists in the table of contents.

Semantics

ARIA roles and epub:type

The following guidance is only for EPUB content documents. The type attribute is the only means of adding structural information to media overlay documents so that features like lists and tables can be navigated more efficiently. It is also required in the EPUB navigation document to identify key structures.

Although the role attribute may seem similar in nature to the type attribute [[epub-3]], their target uses in EPUB content documents do not overlap.

The key difference between these attributes is that the role attribute bridges accessibility in content while the type attribute provides hooks to enable reading system behaviors. Omitting roles lessens the accessibility for users of assistive technologies, in other words, while omitting types diminishes certain functionality in reading systems (e.g., pop-up footnotes or special presentations of the content).

Since each attribute offers different advantages, it is not necessary that they be used together. Due to the lack of restrictions on where EPUB creators can use the type attribute, pairing the attributes may cause accessibility issues (e.g., putting roles on the [[html]] body element).

In particular, the use of the type attribute is not a means of satisfying requirements for ARIA roles in WCAG.

For EPUB creators looking to move from the type attribute to using ARIA roles, the EPUB Type to ARIA Role Authoring Guide guide details notable authoring differences between the two attributes. It also includes a mapping table of semantics in the EPUB Structural Semantics Vocabulary to equivalent ARIA roles in [[dpub-aria-1.0]] and [[wai-aria]].

Do not repeat semantics across chunked content

Although EPUB publications appear as single contiguous documents to users when read, they are typically composed of many individual EPUB content documents. This practice keeps the amount of markup that has to be rendered small to reduce the load time in reading systems (i.e., to minimize the time the user has to wait for a document to appear). It is rare, at least for books, for an EPUB publication to contain only one EPUB content document with all the content in it.

When content is chunked in this way, it often requires the EPUB creator to make decisions about how best to restructure the information. A part, for example, will typically not include all the chapters that belong to it. The EPUB creator will instead separate the part heading from each chapter, putting each into a separate document.

Although visually these restructuring decisions can be hidden from readers, they impact the functionality of assistive technologies. In the case of [[wai-aria]] roles, the result is that only the subset present in the currently-loaded EPUB content document are exposed to users. An assistive technology cannot provide a list of landmarks for the whole publication, as it cannot see outside the current document.

To counteract this destructuring effect, EPUB creators sometimes think to re-add or re-identify structures in the belief that having this information in every document will be helpful to users (e.g., adding an extra [[html]] section element around a chapter to indicate it belongs to a part, or putting the part semantic on the body tag). All this practice does, however, is add repetition that is not only disruptive when reading but can make the structure of the publication harder to follow. EPUB creators are therefore advised not to attempt to rebuild structures in these ways.

For example, consider a book that has five parts and each part contains five chapters. Structurally, each chapter belongs to its part (i.e., is grouped with it), as in the following markup:

<section
    role="doc-part">
   <h1>Part 1</h1>
   
   <section
       role="doc-chapter">
      <h2>Chapter 1</h2>
      …
   </section>
   …
</section>

Since this would lead to a large content file, the part heading is typically split out into its own EPUB content document so that it will appear on its own page:

<html … >
   …
   <body
       role="doc-part">
      <h1>Part 1</h1>
   </body>
</html>

Each chapter is then separated into a separate EPUB content document:

<html … >
   …
   <body
       role="doc-chapter">
      <h2>Chapter 1</h2>
      …
   </body>
</html>

It is not necessary to add a part wrapper to each chapter, as in the following example:

<html … >
   …
   <body
       role="doc-part">
      <section
          role="doc-chapter">
         <h2>Chapter 1</h2>
         …
      </section>
   </body>
</html>

Doing so introduces a new part landmark into each document, which will cause an assistive technology to inform the user that the landmark is available to navigate to.

Include EPUB landmarks

[[wai-aria]] landmarks are similar in nature to EPUB landmarks [[epub-3]]: both are designed to provide users with quick access to the major structures of a document, such as chapters, glossaries and indexes. ARIA landmarks are compiled automatically by assistive technologies from the roles that have been applied to the markup, so EPUB creators only need to follow the requirement to include roles for the landmarks to be made available to users.

Although automatic generation of ARIA landmarks simplifies authoring, it also means that ARIA landmarks are limited to how the EPUB publication has been chunked up into EPUB content documents. An assistive technology can only present the landmarks available in the currently-loaded document; it cannot provide a complete picture of all the landmarks in a multi-document publication (see the previous section for more discussion about content chunking).

EPUB landmarks, on the other hand, are compiled by the EPUB creator prior to distribution, and are not directly linked to the use of the type attribute [[epub-3]] in the content. They are designed to simplify linking to major sections of the publication in a machine-readable way, as reading systems do not scan the entire publication for landmarks, either. EPUB landmarks are typically not as numerous as ARIA landmarks, as reading systems only expose so many of these navigation aids.

Given these differences in application, however, it is important to include EPUB landmarks and not rely only on the presence of ARIA roles to facilitate navigation, and vice versa. Each aids navigation in its own way.

The EPUB specification does not require that EPUB creators include a specific set of landmarks, but it is recommended to include a link to the start of the body matter as well as to any major reference sections (e.g., table of contents, endnotes, bibliography, glossary, index).

Helpful resources

The following resources explain EPUB and ARIA landmarks in more detail.

Titles and headings

Include publication and document titles

[[wcag2]] Success Criterion 2.4.2 requires that each web page include a title. EPUB has a similar requirement for EPUB publications: publications require a [[dcterms]] title element in the package document metadata. The [[wcag2]] requirement is not satisfied by the EPUB requirement, however.

When authoring an EPUB publication each EPUB content document also requires a descriptive title that describes its content. If not provided, assistive technologies often will announce the name of the file to users.

If the title includes structural context (e.g., the part heading a chapter belongs to, or the name of the publication), order the title such that the most precise description of the current document comes first.

For more information about titles, see Technique H25.

Ensure numbered headings reflect publication hierarchy

To a user, an EPUB publication appears as a single document that they read from beginning to end, even though the content is often split across numerous EPUB content documents. As a result, their natural expectation is that the headings reflect their position in the overall hierarchy of the publication, despite the publication not actually being a single document (e.g., if a part heading is expressed in an [[html]] h1 element, each chapter that belongs to the part will have an h2 heading).

Technique G141: Organizing a page using headings instructs EPUB creators on correctly using numbered headings within a document, but with EPUB publications the numbered headings also need to remain consistent across documents. Practically, this means that each EPUB content document does not have to begin with an h1 heading unless the first heading is a top-level heading — the first heading needs to have a numbered heading element that reflects its actual position in the publication.

EPUB creators also to need chunk their content so that the first heading in a document always has the highest number. For example, if a document starts with an h3 heading, there should not be an h2 heading later in the document (e.g., do not include the start of a new section with the trailing subsections of the previous). It is acceptable for there to be subsequent headings at the same level as the first (e.g., multiple subsections in one document could all have h3 headings).

Heading topic or purpose

[[wcag2]] Success Criterion 2.4.6 currently states that all headings must describe their topic or purpose. The implication of this wording is that all chapters in a novel, for example, have a topic or purpose and that the topic or purpose is always clearly reflected by the title of the chapter. Not only is this not always the case, but this success criterion also complicates the use of chapter numbers as headings since these do not establish a topic.

After discussion in the Accessibility Guidelines Working Group's issue tracker, it is clear that the understanding document for 2.4.6 captures the intent of the success criterion better than the current wording — namely, that the requirement for headings is only that they establish a unique context for the content.

By this interpretation, the headings in publications should always pass provided they are unique.

It is expected that the wording of the success criterion will be updated to better reflect the uniqueness requirement, likely in the future WCAG 3 due the complexities of changing the wording for WCAG 2.

Descriptions

Include alternative text descriptions

The first version of these techniques only required alternative text for images regardless of their complexity. This exception is no longer valid.

EPUB creators must now ensure that their image-based content meets [[wcag2]] requirements for alternative text and extended descriptions to conform with [[epub-a11y-11]].

Helpful resources

The following documents provide guidance on including extended descriptions:

Language

Language of package document

[[wcag2]] Success Criterions 3.1.1 and 3.1.2 deal with the language of a page and changes of language with in, respectively.

For EPUB publications, the package document is also an important source of metadata information about the publication. For example, reading systems expose details of the publications to users in their bookshelves using this information.

Consequently, it is necessary to provide the language of all text content in the package document to conform with these WCAG success criteria. The easiest way to meet this requirement is to add an xml:lang attribute on the root package element [[epub-3]].

If individual metadata fields within the package document are expressed in a different language, it is similarly required that the language change be identified by an xml:lang attribute on the element for the field.

Providing this information enables reading systems to correctly render the text content in the proper language for users.

The languages specified in the package document have no effect on individual EPUB content documents (i.e., the language of each document must be specified using the language expression mechanisms it provides).

Language of the EPUB publication

In addition to being able to express the language of text content, the package document also allows EPUB creators to identify the languages of the EPUB publication in dc:language elements [[epub-3]].

Although it is not strictly required to set this information to meet [[wcag2]] Success Criterion 3.1.1, as it is non-normative, it should be considered a best practice to always set this field with the proper language information. (Note that EPUB3 requires the language always be specified, so omitting will fail validation requirements.)

Although reading systems do not use this language information to render the text content of the EPUB publication, they do use it to optimize the reading experience for users (e.g., to preload text-to-speech engines so users do not have a delay when synthesizing the text).

The languages specified in the package document have no effect on individual EPUB content documents (i.e., the language of each document must be specified using the language expression mechanisms it provides).

Text

Use Unicode for text content

[[wcag2]] Success Criterion 1.1.1 requires that text equivalents be provided for all non-text content to meet Level A. In some regions (e.g., Asia), it is not uncommon to find images of individual text characters, despite the availability of Unicode character equivalents. This practice occurs for various reasons, such as ease of translation of older documents and for compatibility across reading systems. The use of images in most instances leads to the text not being accessible to non-visual users, however.

When individual characters are replaced by images, there is invariably a negative effect on text-to-speech playback, even when alternative text is provided (e.g., if single characters within a word are replaced by images, the word will not be read as a single unit of text). It is also problematic for visual users, as the images often scale poorly and the characters cannot be changed to different font families to meet user preferences.

The use of Unicode characters for all text content avoids this problem, allowing content to successfully meet the minimum requirement for Level A.

For compliance with Level AA, EPUB creators are directed to Success Criterion 1.4.5 which further restricts the use of images of text to only a set of essential cases.

Accessible alternatives

As EPUB publications can be composed of more than one rendition, it is possible that different versions of the content will have different levels of accessibility. For example, an image-based version of the content that lacks alternative text or descriptions could be bundled with a WCAG-compliant text-based serialization. This type of accessible bundling is acceptable, as [[wcag2]] allows non-conforming content provided a conforming alternate version is available.

The [[epub-multi-rend-11]] specification defines a set of features for creating these types of EPUB publications. It specifies a set of attributes that allow a reading system to automatically select a preferred rendition for the user or to provide the user the option to manually select between the available options. This functionality technically meets the requirements of [[wcag2]] in terms of ensuring the user can access the accessible version.

In practice, however, the [[epub-multi-rend-11]] specification is not broadly supported in reading systems at the time of publication. As a result, a user who obtains an EPUB publication that contains more than one rendition will only have access to the default. Unless this rendition is the accessible one, the EPUB publication might not be readable by them.

EPUB creators therefore need to use their best discretion when implementing this functionality to meet accessibility requirements. EPUB publications that contain multiple renditions are conformant to the [[epub-a11y-11]] specification if at least one rendition meets all the content requirements, but EPUB creators at a minimum need to note that a reading system that supports multiple renditions is required in their accessibility summary. Any other methods the EPUB creator can use to make this dependence known is advisable (e.g., in the distribution metadata).

This section will be updated with techniques for using multiple renditions when there is enough support in reading systems to broadly recommend their use.

EPUB Techniques

Page navigation

Provide page break markers

Both the EPUB Structural Semantics Vocabulary [[epub-ssv]] and Digital Publishing WAI-ARIA 1.0 Module [[dpub-aria-1.0]] include a semantic for static page breaks: pagebreak and doc-pagebreak, respectively.

It is recommended that both semantics be applied to EPUB 3 content to ensure maximum compatibility with reading systems and assistive technologies.

A title or aria-label attribute is required on the element, as it provides the value that is announced to the user. Do not include the page number as text content, as this practice forces the user to hear it announced wherever it occurs (e.g., without any context in the middle of a sentence).

EPUB 2 does not include markup to identify static page break marks in the content. Page break destinations can be included to enable hyperlinking, but the page list is the only way a user can jump to the locations.

Do not use the [[html]] a element to identify page break locations in EPUB 3 publications. Although this element was previously defined as the anchor for a hyperlink destination, its purpose has been changed in [[html]] for use solely as a link.

Identify pages in audio playback

Readers rarely stop reading to review each new page number, so when page numbers are read aloud in the audio playback of a publication it is not only distracting, but can be confusing, as well (e.g., the number could be read out in the middle of a sentence).

To mitigate this potential annoyance to readers, EPUB creators need to identify page announcements in media overlay documents when they are included. Identification allows a reading system to provide a playback experience where the numbers are automatically skipped.

To identify page numbers in media overlay documents, attach an epub:type attribute with the value "pagebreak" [[epub-ssv]] to each par element [[epub-3]] that identifies a page number.

Note that as EPUB 2 does not provide text and audio synchronization, this technique does not apply.

Provide a page list

A page list — a list of hyperlinks to the static page break locations — is the most effective way for users to find static page locations. Without a page list, the user would have to navigate each page marker in the text, provided they are available and the reading system provides such functionality.

When a page list is included, reading systems can provide users direct access to the list or use it to provide automatic page jump functionality.

The EPUB navigation document allows the inclusion of a page-list nav [[epub-3]], while the EPUB 2 NCX file provides the same functionality through the pageList element [[opf-201]].

Identify the pagination source

Users typically want to know the source of the page break markers included in an EPUB publication when they are derived from a static media. Considerations like which printing, by which publisher or imprint, and whether the pagination comes from the hard or soft cover edition will affect decisions about its usefulness (e.g., does it exactly match the pagination of a print book used in a classroom).

To allow users to determine the suitability of the pagination, identify the ISBN of the source work in the package document metadata.

EPUB 3 allows the source of pagination to be explicitly identified using the source-of property with the value "pagination" [[epub-3]].

The source-of property is particularly useful when there are multiple sources for an EPUB publication as it disambiguates which one the pagination came from.

If an ISBN is not available, include as much information as possible about the source publication (e.g., the publisher, date, edition, and binding).

If the page break markers are unique to the EPUB publication, do not identify a print source.

Synchronized text-audio playback

Ensuring complete text coverage

Ensuring the complete text of an EPUB publication is synchronized with audio is key to allowing users who require full synchronized playback, or even audio-only playback, have access to the same information as users who do not require synchronized playback.

EPUB 3's media overlays feature [[epub-3]] allows audio to be synchronized with any element in an EPUB content document, so there is no technical barrier to providing synchronized playback.

The primary consideration for this objective is what constitutes the text content of an EPUB publication. The minimal candidates for synchronization with audio are all the elements with visible text content.

In HTML, the class of elements called [=palpable content=] [[html]] can typically be synchronized with audio or have their own built-in audio. Embedded text in SVG documents, on the other hand, is found in the text element [[svg]] and its descendants.

The media overlays text element is used to reference these elements, either to play back the pre-recorded audio in a sibling audio element [[epub-3]] or to initiate playback of an audio or video element if the audio element is missing (e.g., for embedded audio and video in the document).

EPUB creators should not synchronize hidden text content in an alternative presentation like media overlays. Synchronizing audio with invisible text will be confusing for sighted readers following the playback.

Text content in a collapsed element, like the details element [[html]], is not considered hidden content.

In addition to synchronizing the visible text, synchronized text-audio playback must also address text alternatives for image-based content. Images may have alternative text and descriptions that are not visible to all users. As synchronization is also meant to aid users who cannot see the images, including these text alternatives and descriptions in the playback is essential to providing the user all the information in the EPUB publication.

Text alternatives and descriptions in HTML may be represented in the alt attribute [[html]] and linked by ARIA attributes (e.g., aria-describedby and aria-details [[wai-aria]]). Descriptions for image elements in SVG are typically represented in a desc element but ARIA attributes may also be used.

Specifying the reading order

The default reading order should typically represent the order in which reading systems render content to users during synchronized text-audio playback. For EPUB publications, this is a combination of the sequence of EPUB content documents in the spine and the order of elements within each EPUB content document.

If there are cases where the logical reading order (how a reader would naturally read the content) diverges from the default reading order, EPUB creators can order the playback sequence of seq and par elements in a media overlays document [[epub-3]] to match the logical order.

EPUB creators need to use caution when making alterations, however, as other accessibility issues can arise when the logical order does not match the default order. For example, the content may not be accessible to users of assistive technologies when the order in the markup does not match how the assistive technology reads the content. In these cases, using playback to create a logical order can make the EPUB publication fail WCAG conformance requirements.

One case where the logical may diverge from the reading order and remain accessible is in tables, as assistive technologies typically allow users to choose whether to read by row or by column.

Identifying skippable structures

Some content elements are not critical to read when following the primary narrative of a work, and that would interrupt a user's concentration if they had to stop and listen to. Footnotes and endnotes are examples of such content, as users may only want to come back and read this content after finishing the EPUB publication. The announcement of page break numbers can be similarly annoying to readers.

EPUB 3's media overlays feature [[epub-3]] does not allow reading systems to determine if playback sequences are skippable unless EPUB creators add additional semantics to the markup, however. EPUB creators must use the epub:type attribute [[epub-3]] to add semantics to seq and par elements [[epub-3]], thereby allowing reading systems to provide users the option to skip their playback sequences.

The recommended structures to identify for skippability are:

  • Endnotes — use the endnotes and endnote semantics [[epub-ssv-11]] for groups of notes and individual endnotes, respectively.
  • Footnotes — use the footnotes and footnote semantics [[epub-ssv-11]] for groups of footnotes and individual footnotes, respectively.
  • Page breaks — use the pagebreak semantic [[epub-ssv-11]] to identify each.

EPUB creators may identify other structures but it is not necessary to meet this requirement.

Identifying escapable structures

Some content elements are containers for expressing complex information. A table, for example, has data arranged in rows and cells. Lists similarly may contain many items. While users may be interested in some of the information in these structures, they also often want to escape from them to keep reading, not have to listen to the entire content before being able to move on. These are called escapable elements, because the user needs to be able to escape from them whenever they choose to simplify the reading experience.

EPUB 3's media overlays feature [[epub-3]] only supports escapability if EPUB creators add structural semantics to the markup. EPUB creators must use the epub:type attribute [[epub-3]] to add semantics to seq and par elements [[epub-3]] to allow reading systems to provide users the option to escape their playback sequences.

The recommended structures to identify for escapability are:

EPUB creators may identify other structures but it is not necessary to meet this requirement.

Identifying nested escapable structures is not recommended at this time. Refer to Escapability [[epub-3]] for more information.

Synchronizing the navigation document

EPUB creators can add a media overlay document for the EPUB navigation document even when it is not included in the spine. Doing so allow reading systems to announce the link labels regardless of how they present the navigation elements to users (e.g., many reading systems applications create custom table of contents panels by extracting the data from the EPUB navigation document).

The process for adding a media overlay document is no different than one for any other document.

Distribution techniques

Do not restrict access through digital rights management

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 digital rights management (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).

In general, DRM can be made to work interoperably with assistive technologies, but problems arise when DRM restrictions remove direct access to an EPUB publication or restrict access to the content within it. Unless the reading system implementing the DRM provides API level access to the content, it can prove difficult, or even impossible, to generate text-to-speech playback, or for a refreshable braille display to have access to the underlying text, as well as cause other accessibility issues.

The application of digital rights management therefore must not impair or impede the functionality of assistive technologies on EPUB publications users have the right to access.

Include accessibility metadata in distribution records

When an EPUB publication is ingested into a distribution system, such as a bookstore or library, a metadata record is often provided separately to the distributor. In these scenarios, the metadata used to enable discovery of the publication typically comes from the distribution record alone, not from the metadata in the package document.

The result is that it is necessary to include as much accessibility metadata in distribution records as their vocabularies allow.

The use of distribution records does not remove the requirement to include accessibility metadata in the package document. The metadata in the package document ensures accessibility information is always available with the publication.

Helpful resources

See the following resources for more information about including accessibility metadata in distribution records:

Change log

Note that this change log only identifies substantive changes since EPUB Accessibility Techniques 1.0 — those that affect the conformance of EPUB publications or are similarly noteworthy.

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