[e] (0) Take some slight risk that we're breaking things, in exchange for an even slighter improvement (using WebIDL instead of a word of prose to explain how to handle the missing argument).
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=20564
Affected topics: DOM APIs, HTML

git-svn-id: http://svn.whatwg.org/webapps@7736 340c8d12-0b0e-0410-8428-c7bf67bfef74