Function pointer 

pub fn pointer(gesture: Gesture, spot: Spot) -> Action

What one mouse gesture means, given what it landed on.

There is no chain here, and that is the point. A key is offered to a list of surfaces because a keyboard has no coordinates; a press has them, so the same question is answered by super::render::hit — an overlay covers what it is over, so a press inside one cannot also be a press on the tree, and one outside is the dismissal.