> I think it would be unfortunate if the feature test macros
> has subtle portability issues of their own.
>
>
> I agree.
>
> Since we seem to collectively have no strong opinions: I think I
> very slightly prefer "expand" over "do not expand" on the basis
> that __has_cpp_attribute(X) and [[X]] should be interpreted the
> same way.

I would prefer "expand" somewhat more than very slightly. :-)

Clark