Now as to documents. The specifics of the Xanadu model are extremely simple. All new content goes into this content layer, not into the virtual documents or versions themselves. The rest is very straightforward. Version-intensive occupations, like law, government and movies, constantly need to find differences and origins among versions.
Many endeavors require the maintenance of conjoined parallel versions for different audiences.
Existing tools are totally irrelevant. Our clean copyright model is based on the sale of fragments and the right to use them virtually in new contexts. This checksums and is manifestly fair. That is the Xanadu model as we have worked on it for decades. For nearly the last decade I have worked to adapt this model to the Internet.