What Is HTML5? HTML5 is a specification (see http://dev.w3.org/html5/spec/) under development by the World Wide Web Consortium (W3C). As we write this book, the HTML5 specification is officially a Working Draft, which means it may go through additional revisions before becoming a recommendation. The recommendation will then go through a formal approval process, resulting in a specific version of the markup language. Meanwhile, independent from the W3C, the Web Hypertext Application Technology Working Group (WHATWG) also pursues development of the HTML specification..... development of the HTML specification.....