Two openings with the same beginning run side by side – recognize when they part.
Two openings run at the same time.
Two openings with the same beginning run move by move side by side, for example Italian and Ruy Lopez. As long as the moves are the same, both boards show the same positions.
Press “Now they part!” (or the space bar) just before the first different move comes. Then you assign each of the two openings its move.