let label_output output =
match output with
| UI_win_opened_event -> H
| UI_win_closed_event(user_window) -> H
| UI_page_loaded_event(user_winndow, url, rendered_doc) -> H
| UI_page_updated_event(user_window, rendered_doc) -> H
| UI_alert(text)-> H
| UI_error(text) -> H
| Network_send_event (domain, req) -> M(domain)