HTML5 introduces HTMLInputElment::valueAsDate, and a JavaScript code can set a value to it. Neither HTML5 specification and WebIDL specification mention what happens in a case of non-Date type object is specified. e.g. input.valueAsDate = 0 input.valueAsDate = "1970-01-01"; WebIDL's editor draft <http://dev.w3.org/2006/webapi/WebIDL/> says HTML 5 uses Date, so we'll need to decide what to do with that. Current thoughts are to be able to state that an interface has a custom mapping to language bindings, and to map that type to a Date in ECMAScript and a java.util.Date in Java. When WebIDl specification has clear binding rules for Date, we should follow it.