Defines a range of directions you can shift these data structures: Scrolling List, Scrolling Tree, Sliding List.
We can visually represent shifting Scrolling List and Sliding List either horizontally (Aback/Ahead) or vertically (Below/Above):
For Scrolling Tree only one representation is avaialable: we can move both horizontally (Aside - switching to a sibling Tree) and vertically (Pitch - climbing up/down through hierarchy levels):