I stumbled across this in an unrelated search for "meta-control." The documentation quality surprised me. Take a look at it yourself for a bit and come back. :)
I found myself interacting with the example before I finished reading about it. The clear section organization of "The meta code..." and "Your goal:" makes it easy to skim. The fact that the goals are very simple--just change an identifier--makes it painless to jump in and modify the example.
If I actually cared about using the system documented here, I would probably do more than change identifiers. :-p
Oops, I couldn't help myself. I put a combo box in my combo box. Broken, but wonderful! XD