I'm envisioning a text format using nesting. Is this a thing?
Say it was used for digital teaching materials. A file might contain an entire textbook worth of text. But rather than linear, or hyperlinked, it would be navigated by starting with a 1 page summary, by human educators. Clicking on any sentence in that page would opens up a paragraph of deeper explanation.
Then another layer again, until opening up all sentences delivers a book-length text.
(1/2)