Taming the wild, wild web
Bill McCoy: EPUB in effect takes the Wild, Wild Web and tames it. EPUB for example requires use of the XML serialization of HTML5 (XHTML5), rather than “Tag Soup” aka “Street” HTML. This means that EPUB content, unlike arbitrary web pages, can be reliably created and manipulated with XML tool chains. EPUB defined Reading System conformance more tightly than HTML5 defines for browser User Agents, pinning down things that are under-specified in the union of W3C standards. [via Patrick Mueller]