XHTML

XHTML is the successor to traditional HTML4, it was the first version of HTML to demand that the document is also correct well-formed XML (although most browsers were not strict about the interpretation). The advent of XHTML (and strong CSS support) allowed for semantic markup to become a reality. XHTML will give way to HTML5 in most cases, although this process will happen according to the level of support for HTML5 in the main browsers, and the speed at which older browsers disappear.