>Rule no. 1: Never, never, NEVER use an index expressions which makes a reference to another table
>Rule no. 2: If you really need an index expressions which makes a reference to another table, see rule no. 1.

I did that a lot... back in the day before we had SQL in FP. That was actually the poor man's join without writing a loop. And that was for temp indexes only.

Other than that, I see no point in this. I also disagree with the originator of this thread that it was possible to open such an index while the related table is not in use. That didn't work eighteen years ago, didn't work meanwhile, doesn't work now.