Function previewed 

pub fn previewed<P: Selectable>(
    reader: &Reader<'_>,
    hit: &PickedElement,
) -> Option<Picked>

What a click on hit would pick as a P in the part reader reads, lit and drawn as it is once held (see Selectable::drawn, Selectable::visuals): so what the pointer lights is what a click holds. None, for a hit that selects none.