Function keep_inside 

pub fn keep_inside(
    size: Size,
    at: Rect,
    work: Rect,
    inset: f64,
    reachable: f64,
) -> Rect

A card the size of size dragged to at, kept inside work and inset from its edges but for a strip reachable long the person can grab: a card that fits stays wholly inside, a card larger than the work area keeps that strip. Every place a card is dropped ends here, so a settled card and a remembered one land the same way.