I spotted something interesting in iTunes 12. If you select one or more tracks, then the Options tab, you can set the Media Kind for files. You can do this to set, for example, videos that you’ve imported as TV Shows or Movies, instead of Home Videos.
In that menu, there is a new Media Kind: Book.
I asked Doug Adams, the AppleScript specialist about it, and he told me he had spotted some new playlists that are stored in the iTunes library: Books and PDFs.
As Doug says, “While I almost certainly have had “PDFs” playlists in the past, this doesn’t appear to be some artifact from a past library. These playlists aren’t in the XML either, but they have persistent IDs and low index numbers. I tried using AppleScript’s delete command to remove them but it didn’t work, which leads me to believe these are hard-coded and are supposed to exist.”
I don’t see why there would be a Book media kind in iTunes, since iBooks handles books (PDF and EPUB), though you can still store PDFs in iTunes (such as for digital booklets that come with album downloads).
Interestingly, if I select a single audio file and check its Media Kind, I don’t see all those options. I only see Music, Podcast, iTunes U, Audiobook and Voice Memo.
Perhaps it’s just a mistake on Apple’s part.