- (when ,ly:moment? "Global time step associated with this column
-happen?")
- (whiteout ,boolean? "If true, the grob is printed over a white
-background to white-out underlying material, if the grob is visible.
- Usually #f by default.")
+ (when ,ly:moment? "Global time step associated with this column.")
+ (whiteout ,boolean-or-number? "If a number or true, the grob is
+printed over a white background that follows the outline of the stencil,
+if the grob is visible. A number sets the thickness of the outline as a
+multiple of the staff-line thickness. For compatibility with former
+behavior (now available with @code{whiteout-box}) the value @code{#t} is
+treated as @code{3.0}. Usually @code{#f} by default.")
+ (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.")