View http://www.iandevlin.com/blog/2013/01/html5/the-main-element
Ever since the HTML5 Boilerplate debut, we’ve all likely been using some form of <div id="main" role="main" /> in our documents. If you took some time to research what the role="main" bit was all about, you’d find that it’s intended to be the main content of a document. Sweet! For various reasons, though, a number of people felt that main deserved to be an element within the HTML5 spec in and of itself. Well now it is.