Function ncplane_move_below 

pub unsafe extern "C" fn ncplane_move_below(
    n: *mut ncplane,
    below: *mut ncplane,
) -> c_int

Splice ncplane ‘n’ out of the z-buffer, and reinsert it below ‘below’. Returns non-zero if ‘n’ is already in the desired location. ‘n’ and ‘below’ must not be the same plane. If ‘below’ is NULL, ‘n’ is moved to the top of its pile.