pub trait ContainerImpl: ContainerImplExt + WidgetImpl {
fn add(&self, widget: &Widget) { ... }
fn remove(&self, widget: &Widget) { ... }
fn check_resize(&self) { ... }
fn set_focus_child(&self, widget: Option<&Widget>) { ... }
fn child_type(&self) -> Type { ... }
fn path_for_child(&self, widget: &Widget) -> WidgetPath { ... }
fn forall(&self, include_internals: bool, callback: &Callback) { ... }
}