what's annoying about that example is that all of those <div>s could be buttons with no other changes. The only content inside the button <div> is the title and folder icon, not the list of examples associated with that title. That's just fine for a button!
The other thing I'd do is add `aria-controls=folder0` to the button that toggles visibility of the list with `id=folder0`
I use them EXTENSIVELY but some don't like them for being annoying to control en-masse with the "toggle all folders" button at the top. But yeah I 100% agree with you. I've snuck them into a webapp where I just needed that much local state rather than have the whole page's state care about the collapse/open state of that one thing.
The other thing I'd do is add `aria-controls=folder0` to the button that toggles visibility of the list with `id=folder0`