Inside any EPUB publication you will find a range of web technologies, but key among them for content production are XHTML5, SVG, CSS and JavaScript. Creating accessible content using these technologies is the focus of this guide, and many of the practices outlined in it are drawn from the work of the World Wide Web Consortium (W3C), the leading authority on accessible web content.
The W3C's Web Accessibility Initiative (WAI, pronounced way) maintains two sets of guidelines covering the creation of accessible web-based content:
The goal of this guide is not to attempt to replace, supersede or otherwise override either of those guidelines, but to function as a means of explaining many of their best practices for EPUB production. (Note: the guide does not attempt to provide complete coverage of either standard, only practices common to ebook publishing.)
Further, subsequent to the original publishing of this guide, the IDPF released the EPUB Accessibility specification. This specification defines formal requirements for producing accessible EPUB publications. The associated techniques explain how to apply WCAG to EPUB publications. Consequently, while this guide remains a useful source of markup practices, it should not be read as anything more than that.
An additional consequence is that the checklist and checkpoints included on this site to help guide accessible production are now out of date. They highlight some key practices, but are not sufficient for evaluating publications to the new accessibility specification. These features will be removed once a formal accessibility checking tool is made available.
Note that this guide also includes information not found in the WAI guidelines (in particular in WCAG). As EPUB currently makes use of XML serialization of HTML5, which is still under development, new WCAG practices have not yet been released to address this content (but the maintainers of this guide are endeavouring to keep the information consistent with evolving practices). There are also many unique features to EPUB, such as PLS lexicons and the Navigation Document, that are not specifically addressed in WCAG or HTML5 at this time. Guidance is continually updated and will be harmonized with future WAI practices as they evolve.
If you are new to accessible publishing, the best place to start is with the free O'Reilly book Accessible EPUB 3, as it will walk you through the basic issues you need to understand in more detail — and with more of an instructional focus. The EPUB 3 Best Practices book includes the information in Accessible EPUB 3 as a chapter, but has also been expanded to include additional information. If you're looking for a more general purpose guide to EPUB 3 production, that also covers accessibility, the Best Practices guide is recommended.
For general how-to questions, please create a new topic in the IDPF accessibility discussion forum.