Hi,
This sounds like a nifty thing, but indeed, is documented in programmer-speak.

I feel your pain, I can’t get it to work either. And that’s after using MODx for years. I tried sticking a number of a document in Default Value of the TV. That just got it to display the child of some other document, and displayed the same one no matter which document I looked at.
Then I tried "@RESOURCE [document number]" as the default value, same thing there. So I’m stuck, too. One question would be, what is "definition", I suppose.
Cheers, Dave