external iter_backward_search:
Gtk.text_iter -> string -> SourceView2Enums.source_search_flag list ->
start: Gtk.text_iter -> stop: Gtk.text_iter -> Gtk.text_iter option ->
(Gtk.text_iter * Gtk.text_iter) option =
"ml_gtk_source_iter_backward_search_bc" "ml_gtk_source_iter_backward_search"