Written Book

Written books are an item created after a book and quill is signed. It appears as the same red book, but without the quill, and has an enchanted-looking glint.

Signing a book and quill
Written books can be obtained by signing a book and quill. After it has been signed, it can not be edited again. The label does not say "Written Book", but what the player titles it. It will say the title on the top line of the label, and "by " on the bottom.  is the username of the player who signed the book. In the Bedrock Edition, this is customizable without commands.

Usage
Written books can be opened by right-clicking (or holding down on the screen on the Pocket Edition), and will display a GUI allowing you to read it or turn the page.

The contents of a book are an extra set of data attached to the item. This means that when a book is destroyed, its contents are lost with it.

Trading
Two written books can be traded to a librarian villager for 1 emerald as part of their tier 3 trades. The two books must be stacked (and therefore must be identical); despite the trading interface having two slots, the villager will not trade for one book in each slot.

Data values
Written books have a data value of 387, and the ID name. They use their item data to determine the contents and some other properties of the book.

Trivia

 * When written books are obtained with commands (without the correct data tag), the label will only show "Written Book" and will have the text "*Invalid book tag*" when opened. The book is signed and cannot be edited without commands.
 * Commands which were added to a written book using serialized JSON objects will be executed through the chat system. This means that any command added to a written book can't be longer than 256 characters, which is the maximum chat line limit.