EPUB 3 Accessibility Guidelines



Assistive Technology (AT)

An assistive technology, in the context of EPUB 3, is either a device or software program capable of rendering content in ways that facilitate reading by persons with disabilities. An assistive technology may be fully integrated into the reading system (an accessible reading system) or may work in conjunction with hardware and software to provide a reading experience better tailored to the reader's preferred modality (e.g., screen-reading software, content zooming technologies and refreshable braille displays).


Content Author (or Author)

The person or organization directly responsible for creating an EPUB publication and ensuring the quality and accessibility of the final product.

Content Provider

The organization directly responsible for providing EPUB content to readers, whether through an online bookstore, corporate Web site, library lending program or otherwise.

Core Media Type

A content format that all EPUB reading systems must support to ensure interoperability of content across devices. All compliant devices are required to be able to process XHTML5 and SVG documents, MP3 and MP4 audio, a variety of common image formats, etc. For a complete list, see Section 5.1 of the EPUB Publications 3.0.1 specification.

An EPUB publication can contain other content formats, but must provide a fallback that is in one of the supported Core Media Types.

CSS (Cascading Style Sheets)

The Cascading Style Sheet language is used to control the rendering of content on reading systems with a visual display screen, but does provide capabilities for rendering in other media such as braille and aural.

CSS Viewport

A screen on a reading system capable of visually rendering the EPUB using the defined CSS styles.


DAISY (Digital Accessible Information System)

The DAISY Consortium is an organization that has been advocating for accessible publishing practices, and that has developed a talking book format specially designed to enable reading by readers with print disabilities. The functionality provided in the ANSI/NISO Z39.86 standard maintained by the Consortium has been fully integrated in EPUB 3.

DIAGRAM (Digital Image and Graphic Resources for Accessible Materials)

The DIAGRAM project seeks to make image and graphic content more accessible by defining a content model for writing descriptions and including alternate representations. More information can be found at the DIAGRAM Center Web site.

DOM (Document Object Model)

The document object model is how the markup content you create gets internalized by a processing agent such as a reading system or browser. Instead of tags and attributes, the DOM is typically likened to a tree full of branches, where each branch represents the parent/child relationships of the document.

When talking about how reading system and assistive technologies interact with content, it is more appropriate to relate behaviors to the DOM, since the DOM is not necessarily an exact representation of the originating content (e.g., a reading system may standardize the HTML markup as it process a document or an assistive technology may enahnce the information to facilitate rendering and interaction).



Any book produced in an electronic format is an ebook. Ebooks may be in EPUB, Microsoft Word, PDF, text, MOBI or a wide variety of other formats.


The ability for non-visual readers to leave the current structure that is being read and continue reading at the next logical spot. Readers will often not want to listen to entire tables and lists being read out, but will expect the reading system to provide a means to jumping out from them at any point.

EPUB is the ebook format maintained by the IDPF.
EPUB Container (or Container)

The container is the ZIP file format and metadata used to bundle all the resources that make up an EPUB for distribution (the .epub file that readers receive when they purchase or otherwise obtain the publication). The container format is defined in the EPUB Open Container Format (OCF) 3.0.1 specification.

EPUB Content Document

EPUB content documents are what get rendered to readers. They can be in either XHTML5 or SVG. Other formats may also be included, but a fallback in one of these two formats is required by the core media type restrictions.

The EPUB navigation document provides structural navigation for readers. The document is designed to be rendered by reading systems for navigation purposes (i.e., the table of contents option offered by the reading system itself), but by using the XHTML5 grammar the documents can also be embedded as table of contents within the publication itself.

EPUB Publication (or Publication)

An EPUB publication is the

EPUB Reading System (or Reading System)

An EPUB reading system is a device capable of rendering an EPUB. A reading system may be a single dedicated device or it could be a combination of hardware and software and assistive technology. An iPad on its own is not a reading system, for example, but when iBooks is run on it the hardware and software constitute a reading system. Discussions about accessible reading systems are complicated by the wide variety of interplay that is possible between devices and software.

EPUB Style Sheet (or Style Sheet)

The CSS styles that reading systems are expected to support. These are defined in Section 3 of tbe EPUB Content Documents 3.0 specification.


Foreign Resource

Foreign resources are the opposite of core media types: resources that are not supported by all EPUB reading systems so require fallbacks. Foreign does not mean that these resources can be hosted outside the container.


HTML5 Outlining Algorithm

A new algorithm defined in HTML5 for creating a document outline from the headings used in a document. Unless enclosed in an hgroup tag, each heading defines a new section, regardless of whether the author explicitly included section tags or not.


IDPF (International Digital Publishing Forum)

The International Digital Publishing Forum (IDPF) is the global trade and standards organization dedicated to the development and promotion of electronic publishing and content consumption.

The work of the IDPF promotes the development of electronic publishing applications and products that will benefit creators of content, makers of reading systems, and consumers. The IDPF develops and maintains the EPUB content publication standard that enables the creation and transport of reflowable digital books and other types of content as digital publications that are interoperable between disparate EPUB-compliant reading devices and applications.



The manifest is the section of the package document that lists all the resources in the EPUB.


A markup grammar for tagging mathmatical equations, enabling both their visual rendering and voicing for more accurate and accessible comprehension.


MathSpeak is natural language grammar for voicing MathML elements.

Media Overlay Document

Media overlays define the sequence of text/audio synchronization points used to traverse the documents in a publication. When the reader turns on playback, the reading system uses these documents to resynchronize the visual display with the audio playback.


NCX (Navigation Control file for XML Applications)

The EPUB 2.0 equivalent of the EPUB navigation document. Although no longer a part of EPUB 3, NCX documents can be included to enable forwards-compatibility in older reading systems that may not recognize all of EPUB 3 but are able to render most of the XHTML content.



OCF is another name for the EPUB container.


OEBPS stands for Open EBook Publication Structure, which was the precursor specification to EPUB 2.0. This acronym was often found used as the directory name where EPUB 2.0 content was stored in the container, but was never required and is not recommended moving forward.


OPS stands for Open Publication Structure. This specification has been renamed to EPUB Publications 3.0. Similar to OEBPS, OPS was often used as the directory name where EPUB 2.0 content was stored.


Package Document

The package document is an XML file that contains metadata about the publication, the resource list (manifest) and the spine.

Package File (or OPF file)

The package document was called the package file in EPUB 2.0. It is still often referred to as the OPF file because of the name of the specification it was defined in in EPUB 2.0 (the Open Packaging Format).

Publication Resource

A resource that is required in order to render the publication. Most publication resources are bundled in the container, but some — like audio and video — can be hosted on the Web.



The person who consumes an EPUB.

Remote Resource

A publication resource that is not included in the container. Audio and video resources are allowed to be housed on the Web because of their potential size. Resources referenced in package document link elements can also live outside the contianer (e.g., metadata records).


Semantic Inflection

Scripted Content Document





SVG Content Document

SVG Viewport


Text-to-Speech (TTS)

Top-level Content Document




WAI-ARIA (Web Accessibility Initiative – Accessible Rich Internet Applications)

WCAG (Web Content Accessibility Guidelines)


XHTML Content Document