LWT JavaScript API
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    Where a save ended up.

    bookId is set when the text was long enough that the server split it into a book of chapters; textId is then the first chapter.

    interface TextSaveOutcome {
        bookId: number | null;
        error: string;
        textId: number | null;
    }
    Index
    bookId: number | null
    error: string
    textId: number | null