DOM L3 Core: Exceptions during DOMErrorHandler.handle and UserDataHandler.handle

There is no description of the expected behavior of the implementation 
if an exception is thrown during an invocation of DOMErrorHandler.handle 
or UserDataHandler.handle.  EventListener has the following as part of 
its description:

    Any exceptions thrown inside an EventListener will not stop
    propagation of the event. It will continue processing any additional
    EventListener in the described manner.

It might be appropriate for an exception thrown in the context of a 
DOMErrorHandler.handle to be equivalent of returning false and for 
exceptions thrown during UserDataHandler.handle to be ignored.