The Up and Down arrows move you up and down the hierarchy of nested boxes; the Left and Right arrows act like "page turners" — Left for the previous box at the same level of the hierarchy, Right for the next one. The easiest way to see how this works is to switch to map view and click the arrows to see where you go. This tool is extremely useful once you already know pretty much where everything is — i.e., how the boxes nest within each other. Then you can move from one "page" to another without having to toggle repeatedly between text view and map view.