<!DOCTYPE html>
HTML5 doctype won’t break your existing markup, because all the tags defined in HTML 4 are still supported in HTML5.
<!DOCTYPE html>
HTML, XHTML, and the HTML DOM. HTML5 is still a work in progress. However, most modern browsers have some HTML5 support.<canvas> element for making graphics with Javascript.<audio> and <video> element for media streaming and playback.localStorage and sessionStorage using the Web Storage interface.email, url, number, range and date.<datalist>, <keygen> and <output>.