In reply to Anh Tran.

That's a legacy feature that I no longer use. I almost dropped it in 2.0 but kept it around for nostalgia. Some of these things go back to a time when child themes couldn't even have templates. These were ideas we were playing around with back then. WordPress' template part system really made this obsolete.

Feel free to copy it from 2.0 if you need it. It's not much code.