Invisible Sun RPG: Enchiridion of the Path - Rules of Play says:
Since the launch of Invisible Sun, players have been asking for more info on the different realms along the Path of Suns. This unique volume is a sourcebook on those realms, but in an unusual format: Its pages consist of dozens of old letters, treatises, arcane notes, and the pages of long-lost books. Each page is a removable handout; this book is a collection of artifacts and game props as well as a sourcebook. The unique binding and perforated pages make it easy to use.