This is what you get when every App has to invent the File System all over again.

My kingdom for a widely-supported cross-platform standard for file metadata and tagging.

How large is it, and does it come with any good-looking princesses?

I'd tell you, but I was keeping all that info in extended attributes and lost it all when I switched filesystems.

It's even worse when media apps are coupled with a store and the cloud. I'm using Apple's iBooks/Books.app as an ePub reader on Mac OS. Searching the library always lands you in the Store portion of the app. The app always forgets the sorting order of the library. And 90 % of the time my epubs are not on the device but uploaded into iCloud; even the placeholder entry is missing its thumbnails. The best way to use Books.app as an ePub reader is to store the books in the file system and delete them from Books.app after reading. But because Books.app is there and free there aren't quality alternative ePub reader for Mac OS anymore.