3 calls to book_menu_subtree_data()

book_export_html in modules/book/book.pages.inc: Generates HTML for export when invoked by book_export().
book_prev in modules/book/book.module: Fetches the menu link for the previous page of the book.
_book_admin_table in modules/book/book.admin.inc: Builds the table portion of the form for the book administration page.

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