Looking for advice on writing Emacs/XEmacs toolbar support

[Stephen Eglen <stephen@anc.ed.ac.uk>]

Does anyone here have any expertise/advice on writing elisp to add
portable (for both Emacs 21 and XEmacs 21) toolbar support to an Emacs
application?  I'm hoping to add a toolbar to the "Emacs Speaks
Statitics" package
(http://www.analytics.washington.edu/statcomp/projects/ess/).  The
code in Emacs 21 (tool-bar.el) looks clear enough, but when I looked a
while ago, XEmacs had a different mechanism for adding a
tool-bar. Since ESS can run on both Emacs and XEmacs, portability is
important.

One option I'm considering is to write a (hopefully) small package
that will abstract away the differences between the Emacs and XEmacs
implementation, which can then be used by other packages.  One
starting point in this direction might be the code from ProofGeneral
(http://proofgeneral.inf.ed.ac.uk) which has code for setting up
toolbars in both Emacs and XEmacs.

I realise this does not directly impact on development of Emacs
itself, so please send replies directly to me rather than the list.

Thanks,
Stephen