EPUB 3 Accessibility Guidelines

Section 508 (US)

This page is provided for informational purposes only. It is not an official document for Section 508 compliance, and should not be referenced as such. The purpose of this page is to facilitate understanding of how to create EPUB 3 publications that meet the Section 508 guidelines.

Section 508 of the US Rehabilitation Act requires that Federal agencies make their electronic and information technology accessible. EPUB 3 publications can be created to meet and exceed the guidelines set out in this legislation for organizations required to meet this mandate, whether federal agencies or organizations that provide products or services to such agencies.

Content creators must be committed to an accessible workflow and follow all best practices outlined generally here and throughout this site, however, as EPUB 3 publications are not accessible by nature of their existence alone.

Section 1194.22 Web-based intranet and internet information and applications.

The following paragaphs of Section 1194.22 apply to all ebook content. Provided for each paragraph is a description of the equivalent EPUB markup practice(s), with links to more information in this guide.

Note that WCAG 1.0 criteria are referenced in the implementation sections as Section 508 only provides a mapping to the older guidelines. See the Additional Resources section for possible mappings to WCAG 2.0.

(a) A text equivalent for every non-text element shall be provided (e.g., via "alt", "longdesc", or in element content).

Text equivalents must be provided for all elements that have no text content, including, but not limited to:

  • images
  • SVG components
  • form elements
  • image map areas
  • inline frames

Text equivalents should also be provided for MathML content for reading systems that do not support voicing.

Note, however, that decorative images and purely formatting elements (like br for manual line breaks and hr for context changes) should not include text alternatives.

(b) Equivalent alternatives for any multimedia presentation shall be synchronized with the presentation.

HTML5 provides the ability to include subtitles, captions and descriptions via the track element to meet this requirement for audio and video content. Captions and subtitles can also be embedded directly into multimedia presentation (e.g., when the object element is being utilised).

In all cases, proper synchronization is necessary to that these alternatives are rendered at appropriate times, but such methods and techniques extend beyond the EPUB format.

(c) Web pages shall be designed so that all information conveyed with color is also available without color, for example from context or markup.

Proper semantic HTML5 tagging — enhanced by the epub:type attribute — will help you achieve this objective:

  • Each structure must be tagged with the most appropriate element(s) to ensure comprehension (e.g., ol and ul for lists, aside for footnotes, etc.).
  • The epub:type attribute should be used whenever applicable to refine the meaning of multi-purpose tags.
  • Never use generic elements that can only be understood by their visual appearance.

Although testing without a style sheet is generally recommended to validate compliance, an equally useful test to ensure compliance is to navigate the EPUB using text-to-speech capabilities to verify comprehension.

(d) Documents shall be organized so they are readable without requiring an associated style sheet.

The proper order of elements in the markup is critical to establishing the logical reading order:

  • Primary content needs to be distinguished from secondary to facilitate navigation (secondary content should be typically be contained in aside, figure and similar elements so that it can be skipped over).
  • Each element that contains part of the primary narrative must follow logically from the one before in the markup file (CSS must not be used to position content visually in a different order).
  • Secondary content should be included in the markup such that it interferes as little as possible with the primary narrative. Correct identification of secondary content will help mitigate unwanted rendering in the primary narrative, however.
(e) Redundant text links shall be provided for each active region of a server-side image map.

Server-side maps are instantiated using the ismap attribute on an image. When this attribute is set, a user agent is expected to send the coordinate location clicked back to the server (to a resource defined in the href of an ancestor a tag). There is no guarantee that an EPUB reading system will honor such behavior, however, as they are not required to be fully-compliant HTML5 user agents. EPUBs are also not guaranteed to be read in an online context, making server-side maps a poor markup choice.

Although there is no functionality that a server-side map provides that cannot be duplicated in a client-side map, there is also nothing in EPUB that bars the inclusion of server-side maps. Adding text links for each region of the map is easily achieved, but such intrusive methods for compliance alone should discourage the use of these less accessible map types.

(f) Client-side image maps shall be provided instead of server-side image maps except where the regions cannot be defined with an available geometric shape.

Client-side maps — using the map element to defined the clickable regions — are the preferred method for including image maps in EPUB 3 both because of online availability issues and because such maps can be made natively more accessible for readers with different preferred modalities.

Each area in the map must have an alt attribute identifying its purpose or function.

(g) Row and column headers shall be identified for data tables.

The th element must be used to identify all table header cells, regardless of whether they occur in the top row of the table, at the beginning or end of each row, or some combination of both. For tables with multi-row headings, the thead element should be used to enclose the header.

Tables should not omit headers and require the reader to determine the meaning from the surrounding context.

(h) Markup shall be used to associate data cells and header cells for data tables that have two or more logical levels of row or column headers.

The headers attribute must be used to when a table cell has a complex table header (e.g., when a cell has more than one header cell associated with it).

The order in which the header cells are identified correlates to how the reading system will announce them, so always include them in logical rendering order.

(i) Frames shall be titled with text that facilitates frame identification and navigation.

Frame sets are not supported in HTML5, removing one obstacle that this guideline was intended to address.

When embedding iframe elements in the content, ensure that each is labelled with a meaningful title that expresses the purpose of its inclusion by attaching a title attribute. Text such as "an inline frame" does not represent a good title.

(j) Pages shall be designed to avoid causing the screen to flicker with a frequency greater than 2 Hz and lower than 55 Hz.

Ensure that no content flashes on the screen at a rate between 2 and 55 cycles per second. This requirement applies to any content that flashes on the screen, including, but limited to:

  • animated images
  • scripted SVG content
  • scripted canvas content
  • scripted text
  • video and other visual playback formats

Although some flickering in video content may be unavoidable, a best practice is to not include any content that flickers, as it is irritating and distracting to all readers.

(k) A text-only page, with equivalent information or functionality, shall be provided to make a web site comply with the provisions of this part, when compliance cannot be accomplished in any other way. The content of the text-only page shall be updated whenever the primary page changes.

EPUB 3 requires that content be fully consumable by the reader, so there should be no need to resort to text-only fallback pages. If a text fallback is being considered, there is likely a better way to accomplish the necessary effect (e.g., progressive enhancement).

When creating SVG-based publications, however, a text serialization in XHTML may be required to fully meet this requirement, as novelization of graphical works is often the only way to fully achieve equivalency.

(l) When pages utilize scripting languages to display content, or to create interface elements, the information provided by the script shall be identified with functional text that can be read by assistive technology.

Progressive enhancement should be used to create fully-accessible scripted publications.

Use of the noscript element is not recommended, as many non-visual readers use JavaScript-enabled devices.

(m) When a web page requires that an applet, plug-in or other application be present on the client system to interpret page content, the page must provide a link to a plug-in or applet that complies with ยง1194.21(a) through (l).

EPUB requires fallbacks be provided for all non-core media types to ensure that EPUBs render across reading systems. In most cases, the proper inclusion of fallbacks will be sufficient.

As EPUB (and HTML5) lacks a standard video codec and container, a link to the appropriate codec may be necessary to comply with this requirement.

(n) When electronic forms are designed to be completed on-line, the form shall allow people using assistive technology to access the information, field elements, and functionality required for completion and submission of the form, including all directions and cues.

The ability to use enhanced HTML5 and WAI-ARIA form functionality — such as the required and aria-invalid attributes — permits content authors to create highly accessible, device-independent forms in EPUB 3 content documents.

(o) A method shall be provided that permits users to skip repetitive navigation links.

This requirement is oriented more toward Web pages than EPUBs, as the aim is to ensure that readers can jump past the repetitive headers and navigation bars on each new Web site page to get to the content.

One case for EPUBs, however, would be to use nav elements and ordered lists to represent all embedded tables of contents. A reader should be able to escape from clearly identified markup such as this if they choose to skip the navigation links.

(p) When a timed response is required, the user shall be alerted and given sufficient time to indicate more time is required.

ARIA live regions can be used to announce to the reader that a time limit is in effect and to indicate the current countdown time, in addition to any visual indicators.

If more time is permitted, the reader must be notified before the expiration. The announcement should be made in a live region to avoid taking focus away from the current activity (an assertive message would be appropriate, since a passive one may not be announced in time).

Ensure the reader can easily extend the time limit, and to return to their current location. The announcement that time is running out should, for example, provide a device-independent method to extend the timer without changing focus (e.g., through a hotkey).

Section 1194.24 Video and multimedia products.

Although not specific to the EPUB format, the following paragraphs are applicable to audio and video content included in a publication:

  1. (c) All training and informational video and multimedia productions which support the agency's mission, regardless of format, that contain speech or other audio information necessary for the comprehension of the content, shall be open or closed captioned.
  2. (d) All training and informational video and multimedia productions which support the agency's mission, regardless of format, that contain visual information necessary for the comprehension of the content, shall be audio described.
  3. (e) Display or presentation of alternate text presentation or audio descriptions shall be user-selectable unless permanent.

Section 1194.31 Functional performance criteria.

The following paragraphs contain requirements to provide alternate modality access to content:

  1. (a) At least one mode of operation and information retrieval that does not require user vision shall be provided, or support for Assistive Technology used by people who are blind or visually impaired shall be provided.
  2. (b) At least one mode of operation and information retrieval that does not require visual acuity greater than 20/70 shall be provided in audio and enlarged print output working together or independently, or support for Assistive Technology used by people who are visually impaired shall be provided.
  3. (c) At least one mode of operation and information retrieval that does not require user hearing shall be provided, or support for Assistive Technology used by people who are deaf or hard of hearing shall be provided.
  4. (d) Where audio information is important for the use of a product, at least one mode of operation and information retrieval shall be provided in an enhanced auditory fashion, or support for assistive hearing devices shall be provided.
  5. (e) At least one mode of operation and information retrieval that does not require user speech shall be provided, or support for Assistive Technology used by people with disabilities shall be provided.
  6. (f) At least one mode of operation and information retrieval that does not require fine motor control or simultaneous actions and that is operable with limited reach and strength shall be provided.

Meeting these requirements will depend on the capabilities of the device the content is to be rendered on (e.g., support for zooming and text enlargement), but EPUB 3 has built-in mechanisms to enable different modalities:

Section 1194.41 Information, documentation, and support.

The following paragaphs of Section 1194.41 also apply to ebooks. Although most of these provisions relate to organizational requirements, suggestions on ways to enhance EPUBs to accommodate are provided.

(a) Product support documentation provided to end-users shall be made available in alternate formats upon request, at no additional charge.

Although an EPUB cannot meet this requirement when the user requests an alternate format, an EPUB does allow a wide variety of modalities to be accommodated without need for specialized formats (e.g., text-to-speech playback, refreshable braille display, etc.).

(b) End-users shall have access to a description of the accessibility and compatibility features of products in alternate formats or alternate methods upon request, at no additional charge.

The ability to include ONIX accessibility compliance metadata in an embedded message is one method EPUB 3 provides to meet this criteria.

(c) Support services for products shall accommodate the communication needs of end-users with disabilities.

This organizational support requirement is outside the purview of EPUB 3, but support for the EPUB itself (the internal contact or trusted intermediary) can be specified in the ONIX metadata.

Compliance References and Standards

Additional Resources