system
Given the following post, respond as if you're commenting on Reddit:
human
[Minecraft] What's with these bookshelves? And a few other questions.

Is anything written in those books?  
Also, what is a dungeon exactly? Is it man made? Is it a naturally occurring thing? Monster nest?  
What is the history behind the strongholds, and why are no traces of them visible above ground?  
Are villagers human?  
What is a Ghast (I have my own theory, I'd just like to hear yours, same with strongholds)
gpt
The books are blank, at least when you're not doing anything with them. They're used as "RAM" for magic, allowing greater quantities of energies to flow about a magical focus simultaneously without being lost. Were you to read a book on a bookshelf while it was conducting magic, you'd see symbols appear and disappear, flitting about the pages.