It was adopted by RIF in the late 80s and was an official rule for Renju World Championships from 1989 till 1995.
The sequence of moves implied by the rule follows.
It is not allowed to pass within the opening stage until the sixth stone appears on the board.
The only difference between these two rules is who makes the second move.
This rule grants this possibility to the second player (tentative white) and RIF rule grants all of the first three moves to the first player (tentative black).