I was just about to ask for that exact thing.
Use-case:
I’m working on a Screenplay C
I need the entire folder to remain open as I go from one file to the next, so I would “pin” the “Screenplay C” folder, and it would display at the top of the navigation pane.
When I know I’ll be spending time working on Scenes I’ll just pin that folder (and I will have all that navigation space to see all the files in the folder). Scrolling down shows more of the files in the folder, but scrolling up stops at the pinned folder.
Writing
Screenplay A
Screenplay B
X Screenplay C
Characters
John
Lucie
grandmother
Scenes
meeting John
eating cake
driving to bar
another scene
and another
Research
item 1
item 2