Function pointed_selection 

pub fn pointed_selection(
    focused: Option<SharedSelection>,
    at: Option<Point>,
) -> Option<SharedSelection>

The one subject rule for what pointing at at is about, given the focused selection: the selection when the person pointed inside it (or did not point at all, with the keyboard); None otherwise, for the caller to name the item under the pointer, else the window. A selection that does not say where it is drawn is not pointed inside.