Function marks_over_copies 

pub fn marks_over_copies(
    copies: &[DeviceCopy],
    shown: &[Rect],
    painted: &[Rect],
    damage: &mut Vec<Rect>,
)

Add to damage what marks painted over a window’s content without moving with it, and unseen by the planner (collaborators’ pointers and names), cost its copies (device pixels, as each would be repainted): the target holds the marks of the frame on screen (shown), which a copy moves with the content, stale, one delta away; and this frame’s marks (painted) must be repainted wherever a copy wrote under them. Where a mark changed in place is the frame’s other damage, carried with it (carry).