Mastodawn

Yes, it does.
Very much so.
For nearly thirty years.

Kudos to Kent Pitman.

[email protected]> the specific macro expansion can differ though, right?

Yes, and it often does (and it may well contain implementation-specific items, of course).

And `macroexpand' is certainly a good way to explore things; just consult the specification as well (in this case the excellent Hyperspec, CLHS).