I'm not sure that the current concept of return converters in AC is can be used for specifying return value annotations.

For example, what if I want to annotate the return value type with using a return converter?

Another example: The current doc-string for select.select() begins with:

select(rlist, wlist, xlist[, timeout]) -> (rlist, wlist, xlist)

I can't see how describing the return type being a 3-tuple of lists would work with return converters.