These doors usually have even numbers of leaves and meet at the center of the building opening. They operate by telescoping toward each side of the building opening, typically into door pocket structures located beyond the extents of the opening. The lead leaf of each door group contains the motor operating system and drives the remaining leaves in the group. The doors in a group can be interconnected with the drive leaf by a linear cable sheave system (known as an anchored group) or by a system of pick-up brackets.