@mutahhir Great to see you pushing FoldingText forward. Nice work!
Let me preface this request with the the fact that if I’d implemented this feature I would have just included headings in the list, and from the feedback that I’ve seen people really like the modes feature. So nice work AND take my suggestions as just things to consider, because you are already making great decisions.
Anyway I think the feature overall is great. It helps expose FoldingText’s underlying feature set in a very simple way. My complaint is that I think visually the list text should either match the body text more closely (differing on just one attribute), or it should match the default system font styling for sidebar text. In the current styling it uses the same typeface as the body text, but different size, color, and linespacing. I think all that difference makes it not fit ideally into the rest of the UI.
Instead I think it would be better to pick just one attribute typeface, point size, color, or line height (or some other style, bold, italic, etc) and see how that looks.
Or alternatively you could copy the default OS X sidebar font style. Which different on lots of attributes, but matches the OS X style, so it is still expected and fits on.
Even if you decide not to do the above in the current styling I have a hard time picking out the different levels in the hierarchy. For example if I open the users guide it’s a bit hard to see the structure by glancing at the sidebar. I think increasing the indents or decreasing the line height (or both) would help in that respect.