If position is out of bounds, it is assumed to be the current number of pages. Pages are numbered starting at zero. Switches to the next page. Nothing happens if the current page is the last page. Switches to the previous page.
Nothing happens if the current page is the first page.
Out of bounds position will be clamped. Bookmarks are in the border. Returns the page number of the current page. NULL is returned if child is not in notebook or NULL if it has the default menu label. NULL is returned if child is not in notebook or NULL if it has the default tab label.