For your perusal, here's a video of Ted demonstrating Xanadu: [0] (3min18sec to jump right to the demo)

You can also browse the book he published describing the system, Literary Machines (1981) [1] -- it's a sprawling vision but I think where the parent sees overlap is in storing each text fragment as a singular entity and visualizing the links between two fragments.

> A user may also make side-by-side connections of other types. On contemplating any two pieces of text, he may make a link between them. Thereafter, when he displays either piece of text, and asks to see the links, a link-symbol is displayed, and the other attached text — if he wishes to see it.

> Naturally, making a marginal note consists of writing the note and hooking the link. The link facility gives us much more than the attachment of mere odds and ends. It permits fully non-sequential writing, or hypertext.

BTW I really like the interface of just typing and moving my cursor around, and how easy it is to pick up a block of text and move it somewhere else.

[0] https://youtu.be/En_2T7KH6RA?t=203

[1] https://archive.org/details/literarymachines00nels_3/page/n6...