i don't know that this is really practical, or any more practical than
simply stating what specific rule changes from FIDE a particular variant
has on the page of it's original listing. Isn't FIDE Rule Zero enough?
Also, along the lines of Thomas's sugesstion, a more useful
compilation might prove to be a Zillions scripted Piececlopedia.
Considering the wealth of work Ralph's done, surely by now most of the more
common pieces are presently defined in zrf terms somewhere. Now THAT would
be a time saver!
Instead of hunting through endless variants to see how a certain piece
might be defined, have all of them gathered in one file that could be
copy/cut/pasted from into a new variant. We could even have a user rating
as to which specific manner of scripting a certain piece proved to be the
most effective; additionaly things like castling under all the variously
described conditions could be included also.
IMHO.