Can it be done? Sure it can! But it requires a few minor adjustments..
1. Alter your master page to allow HTML5
Edit the masterpage of your site in Sharepoint Designer. Locate the following tag:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
Simply remove everything behind “html” except the closing tag:
2. Remove forced IE 8 rendering
Your masterpage has a tag that pretty much says “Force this page to be rendered as an IE 8 browser would”. But IE 8 doesn’t support HTML 5 so get rid of it – delete the following line from your masterpage:
<meta http-equiv="X-UA-Compatible" content="IE=8"/>
3. Back in your Sharepoint site, add a new Content Editor webpart on the page where you want the magic of HTML 5 to be displayed. Open the HTML editor for the contents (you’ll find it up at the ribbon, looks a little something like this:
4. Put your HTML 5 code into the HTML Source window that appears, click OK and Bob’s your uncle!