/// A retained-UI system: it runs on the ECS group directly, so it works whether
/// the host drives it in the frame schedule or a test scripts it. Owned by the
/// UI crate, which defines the schedule these go in.
pub use UiSystemFn as SystemFn;
/// The retained-UI pipeline systems, in run order. The frame's post-update
/// stage drives them through
/// [`run_retained_ui_schedule`](crate::plugins::ui::run_retained_ui_schedule),
/// right after transform propagation. Composing
/// [`UiPlugin`](crate::plugins::ui::UiPlugin) populates the list with
/// [`ui_systems_with`](nightshade_ui::ui_systems_with).