Function anchored

pub fn anchored<Msg: Clone>(
    child: impl Into<Element<Msg>>,
    anchor: WidgetId,
) -> AnchoredOverlay<Msg>

Draw child right under the widget whose .id( … ) is anchor, as it was laid out on the previous frame: a menu under the button that opens it. Until the anchor has been drawn the child fills the rect its parent gives it.