Usually, the tail of the traveler line is dead-ended with a knot on the block mounted on the traveler car, and that’s it. But here, after the knot, a long tail goes up through the mainsheet block then down to the traveler car block on the other side. The other side looks identical to the side shown in the photo.
One piece of line takes care of the entire traveler car purchase, on both sides. Apart from being very clean, this simple system helps hold the block upright, keeps it aligned 90 degrees to the traveler, allows it to be mounted closer to the car and eliminates some of the problems associated with stand-up springs.