A Jackline eliminates the need to go to the mast during a reef. Reef from the safety of the cockpit. Standard on all Catalina Direct Mains'ls

The bottom luff slides are attached to the sail via the Jackline. When the sail is at full hoist, the Jackline is tight and the sail is held against the mast. When you reef, the jack line goes slack allowing the reef cringle to reach the gooseneck.