I have several examples. Here's the simplest one. I would not expect to see the "left inner do" message at all. And I would expect that, in the end, i and j are both 1. But ...
v:\> type leaven2.btm do i=1 to 2 do j=1 to 2 leave 2 enddo echo left inner do enddo echo i = %i and j = %j v:\> leaven2.btm left inner do left inner do i = 3 and j = 1