What is the "Story bible" box when creating a new book?

On the last step of the New Book wizard there is an optional box called "Story bible". Write anything the AI must know before it starts — character names and traits, world rules, background facts, terminology. Unlike a regular prompt, this text is stored with the book (in its Codex) and is treated as authoritative facts for the WHOLE generation, starting with the very first outline. After the book is created you'll find the text in the book's Codex under Knowledge ("Author notes"), where you can refine or extend it any time.