While Gnus runs under Emacs, XEmacs and Mule, I decided that one of the platforms must be the primary one. I chose Emacs. Not because I don't like XEmacs or Mule, but because it comes first alphabetically.
This means that Gnus will byte-compile under Emacs with nary a warning, while XEmacs will pump out gigabytes of warnings while byte-compiling. As I use byte-compilation warnings to help me root out trivial errors in Gnus, that's very useful.
I've also consistently used Emacs function interfaces, but have used
Gnusey aliases for the functions. To take an example: Emacs defines a
run-at-time function while XEmacs defines a
function. I then define a function called
takes the same parameters as the Emacs
run-at-time. When running
Gnus under Emacs, the former function is just an alias for the latter.
However, when running under XEmacs, the former is an alias for the
(defun gnus-xmas-run-at-time (time repeat function &rest args) (start-itimer "gnus-run-at-time" `(lambda () (,function ,@args)) time repeat))
This sort of thing has been done for bunches of functions. Gnus does
not redefine any native Emacs functions while running under XEmacs—it
defalias thing with Gnus equivalents instead. Cleaner
In the cases where the XEmacs function interface was obviously cleaner,
I used it instead. For example
gnus-region-active-p is an alias
region-active-p in XEmacs, whereas in Emacs it is a function.
Of course, I could have chosen XEmacs as my native platform and done mapping functions the other way around. But I didn't. The performance hit these indirections impose on Gnus under XEmacs should be slight.