Function walk_subtree 

pub fn walk_subtree<D, V>(
    dom: &D,
    root: D::NodeId,
    visitor: &mut V,
) -> ControlFlow<V::Stop>
where
    D: LayoutDom + ?Sized,
    V: NodeVisitor<D> + ?Sized,

Walk root’s subtree with visitor, descending via LayoutDom::dom_children. Returns ControlFlow::Break(stop) if any visitor method bailed; otherwise ControlFlow::Continue(()).