Function UnhandledKeyEvents 

pub fn UnhandledKeyEvents(handler: impl Fn(&KeyEvent) -> bool + 'static)

Hands handler every key event no control took: none was focused, a focused control let the key pass, and no text field is taking typing.

This is where an application puts the shortcuts that work anywhere in it, a media player’s play and stop keys, for instance. The handler returns true for a key it used. While several are composed, the one composed last is asked first, and a key goes no further once one takes it.

UnhandledKeyEvents(move |event| {
    if event.event_type != KeyEventType::KeyDown {
        return false;
    }
    match event.key_code {
        KeyCode::X => { play(); true }
        KeyCode::V => { stop(); true }
        _ => false,
    }
});