Graph of contents
A graph of contents is a more structured alternative to a table of contents.
Clicking on a dotted link brings up the graph. The label for the current section (as identified by the link used to bring up the graph) is bolded in the graph. Clicking a label in the graph hides the graph and scrolls to that section in the document. Clicking the background just hides the graph.
You can reorganize the graph by dragging a node to fix it into a position. For example, if you were skipping around in a large document, you could track which sections you’d read by dragging their nodes to the right margin. Double-clicking releases a node that’s been fixed in place.
This technique can be found in vivo in the post on biblometrics.