Martin Buchholz <martin(a)xemacs.org> writes:
FSF has a policy of never looking at XEmacs source code because of
copyright purity contamination issues. The only way you can
contribute to FSF Emacs is by signing a copyright assignment and
submitting patches directly to the FSF team.
In some cases it's also possible to contribute code to XEmacs, assign
the contribution to the FSF, and mail it to them for inclusion to GNU
Emacs. But they (Stallman at the time) were highly suspicious of
that kind of cooperation, and accepted it only grudgingly.