RE: Bikeshedding go! Why is <M-f4> unbound?

[Drew Adams]

> unless ... "the user says he doesn't like it", it should be
> allowed to fall through to the fallback when the Emacs
> binding is void.

I argued that the user (and libraries) should be able to not only bind the key
(which no one has disagreed with) but also specify what to do if it is unbound:
raise an error or pass it through to Windows.

That's feasible with Stefan's proposal (assuming implementation details can be
addressed, which need to be addressed anyway for the pass-through).  And it
gives users and libraries the choice, at runtime, that you are trying to make
here, at design time.  Not only least astonishment but most control.