- (whiteout-box ,boolean? "If true, the grob is printed over a
-rounded rectangular white background to white-out underlying material,
-if the grob is visible. Usually @code{#f} by default.")
+ (whiteout-box ,boolean-or-number? "If a number or true, the grob
+is printed over a rectangular white background to white-out underlying
+material, if the grob is visible. A number indicates how far the
+outline extends beyond the bounding box of the grob as a multiple of
+the staff-line thickness. Usually @code{#f} by default.")