Self Referencing Book

Why?

Help you remember the what and who of a book that is complex or you continue reading after a long break.

How?

Have an option in ebook readers to turn on a layer of hyperlinks. These should be available to link characters and events mentioned to their origin in the book, so you can click on such a link, and it will either take you to the source so you can catch up again, or pop up a window with the original text so you can take a look, close it, and continue reading.