Please consider taking “collapse feature” one level deeper. So if I double click on a Headline it would also collapse what is within it.
What I envision about your tools is related to research. Right now Im studying a program and it has different modules. The “Business Category” has “webinars” as the Project. Within Project I have various research. I can collapse each research but in my case I have lots of Modules to study.
Based on your current model the only next ‘layer” I can have is a Headline then subheads. So if I could collapse the Headline content under it it would allow me to have a much larger organized system without getting overwhelmed looking at so many notes for each module. (each headline would be a module) Each training program can have many videos per module so the amount of note takeing can get unrulely as you might imagine.
If you know a better way to organize my note Im all ears. I think your new tool has a lot of promise. Well done!