EPUB 3.3 becomes a W3C recommendation
w3.org
w3.org
(you'd think maintaining an epub extension for a web browser wouldn't be that much of a stretch, considering that epubs are built on web tech, but who knows why they cut that.)
Massive refactoring and simplification of overlapping sub-specs
Support for webp and opus
Accessibility improvements including EU compliance (not sure if that's referring to the updated format or the text of the spec itself)