In my last post on Program Object Models, I was trying to figure out how to replace the Notepad functionality of the 1990s-era Ecco Pro PIM program with a more modern version. It turns out that my desired multi-collapsible outline, that I liked so much in Ecco Pro, is present in OneNote.
In OneNote, as you mouse over a line, a box with a four-way arrow appears to the left. If you double click the box, any child items collapse. Another double-click reverses the process. Additionally, the collapsed state of the child items is sticky, so they show up the same as before. This functionality is vital when you bury lots of detail deep in a hierarchy, but you do not want to see it all the time.
It looks like I will be using OneNote to build the outline for my desired object model. Now, I can delete Ecco Pro once I copy everything over to OneNote. Ah, Ecco Pro, I knew you well...