Using tal:attributes with tal:replace="structure context/submit" 
doesn't actually add attributes to the resulting submit button.  This 
makes it impossible to style the button by adding a class attribute.  
The reason this happens is that context/submit returns two or three 
hidden inputs before the submit input.  The attributes assigned by 
tal:attributes get attached to the first (hidden) input instead of the 
submit input.  The fix is to make the submit input get returned first 
in the HTMLClass.submit and _HTMLItem.submit methods in templating.py.