Book details
Runs entirely in your browser — nothing here is uploaded anywhere.
Advanced
Leave this off unless you specifically need it — it tells the server the text was already processed, which normally happens automatically when a player or lectern opens the book.
Pages
Over 100 pages — that's beyond the normal in-game writing limit, but a command can still create it.
Click a color with nothing selected, then type — everything stays that color until you click another one. Drag over existing text to restyle just that part. For click/hover events, select some text first.