Lectern/BE


 * Block entity data
 * : The book item, without the slot tag, currently on the lectern, may not exist.
 * : The page the book is currently on, starting from 0, does not exist if there's no book.
 * : The page the book is currently on, starting from 0, does not exist if there's no book.
 * : The page the book is currently on, starting from 0, does not exist if there's no book.