Re: [TreatNonCallableAsNull] alternative?

Boris Zbarsky:
>>> If you're writing IDL for something that's already in the wild
>>> with this behavior, you need it.
>>>
>>> If you're writing a spec for something new, you don't.

Anne van Kesteren:
>> Are you sure?
>>
>> I think we'd want all event handler attributes to behave the same
>> way.

Marcos Caceres:
> That would be nice … [TreatNonCallableAsNull]'s behaviour is actually
> quite nice and forgiving (which is why I wanted to use it in the
> first place).

Which event listener attributes do we actually *need* it for currently? 
  Is it a set that might creep to become bigger?  Consistency across all 
event listener attributes seems nice to me, but I admit it is trading 
off against hiding authoring errors.

Regardless, I don't think we want to allow [TreatNonCallableAsNull] 
behaviour elsewhere.  It's not consistent with how type conversion is 
done elsewhere.