"Golubev I. N." <gin(a)mo.msk.ru> writes:
The main question is: if one wishes to `make a nontrivial
contribution' to XEmacs, what legal formalities are required from
him according to XEmacs project policy?
None.
If you wish, you can assign your changes to the FSF, in which case the
GNU Emacs maintainers can choose to use them. While such an
assignment is beneficial for good relations between the development
groups, it is not obligatory.