Isn't that the one used in Gimp? It's similar to Guile, I think. My apologies for not following the discussion closely, but if it's lisp vs xml, I'd vote for lisp, and even promise to provide the C side of the tie-in. And Guile, in my opinion, would be a great choice for either problem; I think it is presented as "an extension language" -- the scripting business comes for free, and wasn't to the point anyway. But XML seems to be everywhere -- so is Windows...