[WebIDL] overloading string/null/object

If I have

   x(in DOMString y);
   x(in Document y);

do I need to put [Null=Null, Undefined=Null] in front of "in DOMString" or  
will this work correctly automatically?


-- 
Anne van Kesteren
<http://annevankesteren.nl/>
<http://www.opera.com/>