> Is it possible to play around with it a bit (that, and nothing more, is
> what I'd like to do) without being an X11 guru? Any documentation, any
> tutorials for other languages that can be applied do Ruby/X11, too?

Very readable, clean code, still, you should know at least the basics
of X11 for it to be useful to you.

Keep in mind it was written originally for an older Ruby version 
(1.6.4  if I remember well, please correct me Mathieu if I'm wrong)

Still, I don't understand what you mean by "tutorials for other
languages that can be applied"

Ruby/X11 is entirely written in Ruby, to be used from within Ruby
programs, but of course there's plenty of other things that can be
done on top of it, imagination is the limit.

cheers,
                     vruz