string/xor.rb file should probably be called op_xor.rb instead. That's the going procedure so that facets-live.rb will be able to convert operators to names. Hover someone mentioned it seemed rather redundant to use "op" prefix. Perhaps these methods could just have names without the the prefix?
If there are no significant naming conflicts, then getting rid of the op prefix is a possibility. In the mean time a op_xor.rb alias to xor.rb will do the trick.