I use the Alfred Series to teach piano to my students. I would gladly buy every book in the series, Lesson, Recital, Theory.....if only they could be marked on, notes and highlights. Otherwise this is extremely frustrating. Even just making certain selections openable in another app like GoodNotes where you can mark your pieces. Or sell them as apps themselves. I see the problem in making them available that way, but it's the only way this would work. Hope maybe in the future there is a solution for that.