HTML5 DocType support

I am developing an ASP.Net Web User Control that uses the HTML5 DocType that is the default DocType support in Visual Studio 2012.

However, when I go to publish this User Control and add it to my Sitefinity page,it invalidates my user control because of my HTML5 specific form fields.  However, all of my end users will be using HTML5 compatible browsers, so why is Sitefinity blocking me from using HTML5 compliant form fields in my Sitefinity pages?