Notch created books and bookshelves, but it has always been a decorative item, and is relatively useless. I think you should be able to write in books and place them in bookshelves, similar to wurskniftes Bookmod. It would be simpler, so that there would only be one type of book, and books wouldn't be stackable at all. To write in a book, you would need a pen, which you would craft with a feather and an ink sack. Pens should have durability, so only a certain amount of letters can be written. Erasing letters wouldn't restore durability. When a pen runs out of durability, it would become a feather and you could put more ink on it. I hope you consider this idea to be added to the game.
Thanks for all the feedback and support! I also think this would help alot with servers, so you wouldn't have to put down a bunch of signs for rules, you could just make a rulebook. That gives me another idea. Books that can be duplicated and making some books so they can't be edited.
I definitely think this should be implemented. When Mojang added maps I was almost certain this was to test the process needed to implement custom books.
“You cannot strengthen the weak by weakening the strong" -Abraham Lincoln
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