On Rich-Substrate Books

For digital books, we are no longer bound by the medium of text only. Hypertext is a good start to the ways we can make content more digestible. Another step to take is to define various “views” for the same content. For example, a textbook could have, amongst other, a "learning" and a "reviewing" view. In the learning view, definitions are supplemented with comments and more exercises are visible, while in the reviewing view, only those things necessary to refresh the memory are visible.