the #GtkWidget to use as the contents of the page
the #GtkWidget to be used as the label for the page, or %NULL to use the default label, “page N”
the widget to use as a label for the page-switch menu, if that is enabled. If %NULL, and @tab_label is a #GtkLabel or %NULL, then the menu label will be a newly created label with the same text as @tab_label; if @tab_label is not a #GtkLabel, @menu_label must be specified if the page-switch menu is to be used.
the index (starting at 0) at which to insert the page, or -1 to append the page after all other pages.
Return: the index (starting from 0) of the inserted page in the notebook
Insert a page into @notebook at the given position, specifying the widget to use as the label in the popup menu.