Also, as far as I can tell, there's no way to set a radix for an html5 input type, so supporting this would be a step beyond what html5 input types actually do... I don't necessarily see that as a bad thing, however it's complicated, and users don't really have a way to ask for a specific radix (and if they did, and tried to enter a hex number, a browser with HTML5 constraint validation would call it invalid anyways)