Release tested: 10.3.9
The following loop did not produce any output. It worked correctly without the REVERSE key word.
With the REVERSE key word, switching the lower and upper bound values also worked:
FOR idx IN REVERSE 10..loop_start LOOP
However, this behavior is different from Oracle's documentation below.
If REVERSE is specified:
If upper_bound is less than lower_bound, the statements do not run, and control transfers to the statement after the FOR LOOP statement.