Authoring content for digital books

This disclosure describes systems, methods, and computer program products for authoring content for digital books. In some implementations, a single graphical user interface (GUI) is presented that allows an author to design a layout for the digital book, including editing text and inserting various types of interactive elements in the text. The GUI functions as both a digital book layout design tool and a word processor to facilitate the building of a digital book. The relative page location of inserted widgets can be determined by a user-selectable anchor point placed within the text. An outline view of the digital book can be created and presented in the GUI based on a hierarchical structure determined by paragraph styles applied to the text. The GUI can provide a hybrid glossary and index page for allowing the author to create and manage a glossary and index for the digital book.