Function find_mut 

pub fn find_mut<T>(root: &mut dyn Widget) -> Option<&mut T>
where
    T: Widget + 'static,

The first widget of root’s subtree, root included, that is a T, to change: a view or a page wraps the widget it places (a row’s swipe around its row, a docked page around its list), so a caller reaches it wherever it sits.