HTML5 controls not in enabled in vs11?

Hi,

I've a standard asp upload control in standard asp webform in visual studio 2012

Now I've stript the

<!DOCTYPEhtmlPUBLIC"-//W3C//DTD XHTML 1.0 Transitional//EN""http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

to

<!DOCTYPEhtml>

The problem is that i still don`t have the property AllowMultiple="true" in the upload control...I don`t want to use the input control..

Does someone knows what i need to do to get the html5 controls enabled?

Best regards,

Mark