indexes are lists. While they do state relationships they are not the type of document that would bear any significant content. Nor are they easily integrated into a document with content. An example of what this would look like would be a Wikipedia page that had all hyperlinks listed on the side and relationships between the hyperlinks annotated with marks like BT, NT, and RT. While the reader could figure out relationships they would be less visually discernable than more prominently displayed links between concepts in a given page.