gdk:toplevel-size-set-shadow-width (size left right top bottom)

size -- a gdk:toplevel-size instance
left -- an integer with the width of the left part of the shadow
right -- an integer with the width of the right part of the shadow
top -- an integer with the height of the top part of the shadow
bottom -- an integer with the height of the bottom part of the shadow

The shadow width corresponds to the part of the computed surface size that would consist of the shadow margin surrounding the window, would there be any.