Originally Posted by
rpenmanparker
I guess I understood that. I think the best bet is to just assume incompatibility except in the very few well publicized cases of known compatibility. Examples are the 8-speed Shimano RDs and 9-speed levers and the SRAM 10-speed RD with 11-speed levers.
Sure, but it's always nice to be able to use cheap/free components when you can rather than use the one you're supposed to. I mix and match on 3 of my 5 bikes and it works great.