A lot of details haven't been explained clearly, as far as I know, but the basic idea is in Nelson's books.

There's no embedded markup. Links and formatting is off to the side in other documents, referencing locations in the original document.

You also have "transclusions," where you say "in document A position A.n, embed part of document B from position B.n to position B.p."

By using transclusions, you can make new versions of documents, without messing up the links and formatting codes even though they aren't embedded and reference by character position. Because you're not editing any original documents, anyone can effectively make changes. You can add a link to a page without even making a new version, you just put a new link in a side document.