The Accessible Publishing Knowledge Base was originally conceived as a complement to the O'Reilly Accessible EPUB 3 ebook published in 2012. It was a way to surface all the information that was collected as part of authoring that book but that could not all be added to it.
DAISY has continued to develop the site since that time, and it now covers an extensive range of topics on creating accessible digital publications. While still primarily rooted in making EPUB 3 publications accessible, the site is also a source of accessible practices for EPUB 2 and also provides practical guidelines for creating accessible HTML content in W3C Audiobooks.
The intervening years have also seen the publication of the EPUB Accessibility specification, which defines a formal framework for checking the accessibility of EPUB 3 publications. This site is now a primary source of information for producing content to meet this specification.