Longer than its frame, so a view can be moved across it. Of a thing whose whole cannot be seen at once.
From scroll (Old French escroe, a strip of parchment), with the suffix -able; naming a thing whose whole cannot be seen at once but can be reached by moving through it.
Marking a thing whose whole cannot be taken in at a glance — there is more here than the frame shows, and it can be reached by moving through it.