The feature, known as "Collections," allows customers to add their content to multiple categories instead of just one. For example, "A Game of Thrones" can be included in "My Favorites" as well as "Fantasy Epics."
The company also tweaked the app's design around the themes of "deference, clarity, and depth." The flatter-style controls provide a sharper appearance, while translucency effects "keep constant connection between customers and their content." The library and reader also feature slide-out menus that combine key controls and glide to the touch.
The update comes as Apple launches iOS 7, the latest version of its mobile operating system. The software is going out to users as a free update Wednesday, a little more than a week after developers got a finalized version, and some three months after Apple first showed it off back in June. Changes include a complete visual overhaul, as well as the iTunes Radio music service and an overhauled version of Siri.