let page_update_event (pr: page_ref) (b: b)
: output_event =
let wr =
begin match page_win pr b with
| None -> assert false
| Some(wr) -> wr
end
in
let uw = win_to_user_window wr b in
let rd_opt = render_page pr b in
UI_page_updated_event(uw, rd_opt)