Function closed_dropdown_keys 

pub fn closed_dropdown_keys(
    keys: MessageReader<'_, '_, KeyPressed>,
    tick: Res<'_, Tick>,
    config: Res<'_, PopupNavConfig>,
    type_ahead: ResMut<'_, TypeAheadBuffer>,
    tracker: Res<'_, FocusTracker>,
    headers: Query<'_, '_, &DropdownButton>,
    store: ResMut<'_, PropertyStore>,
)

Closed-combobox keyboard interaction on the focused dropdown header. Uses the option metadata mirrored onto DropdownButton (the panel body may never have mounted). See the module docs for the exact Qt contract.