Thanks for the plugin, I really enjoy it.
One little nagging frustration, though:
I can choose the text to be either horizontal or vertical. However, it would be great that there’s a third option to make the text vertical for currently hidden/collapsed panes, and horizontal for those that are in view (or at least for the focused one).
Another quality of life improvement would be the ability to preview the vertical title of a collapsed pane in horizontal, when hovering with the mouse pointer over the title. The title would pop-out in horizontal.
This would help by avoiding the need to rotate my head all the time so that I can actually read the document title–or keep all the titles horizontal, and then being unable to read them on collapsed panes.