Feature for being able to collapse the table of contents based on Heading level. So if I have a bunch of Heading level 2 I can just collapse to Heading level 1 and see all of headers of Heading 1 on the table of contents instead of the need of scrolling down to the Heading 1 header I need. Even if it was just Heading 1 to collapse, that would be a major help as it would give top level view of what information the page contains.