-The distance between the current staff and the staff just below it
-in the same system, even if one or more non-staff lines (such as
-@code{Lyrics}) are placed between the two staves. Does not apply
-to the bottom staff of a system. This replaces any settings
-inherited from the @code{StaffGrouper} grob of the containing
-staff-group, if there is one. If this is unset, and there are no
-@code{StaffGrouper} properties to inherit, the
-@code{default-staff-staff-spacing} property is used.
+
+Used to determine the distance between the current staff and the
+staff just below it in the same system, even if one or more
+non-staff lines (such as @code{Lyrics}) are placed between the two
+staves. Does not apply to the bottom staff of a system.
+
+Initially, the @code{staff-staff-spacing} of a
+@code{VerticalAxisGroup} is a Scheme function that applies the
+properties of the @code{StaffGrouper} if the staff is part of a
+group, or the @code{default-staff-staff-spacing} of the staff
+otherwise. This allows staves to be spaced differently when they
+are grouped. For uniform spacing regardless of grouping, this
+function may be replaced by a flexible-spacing alist, using the
+complete-redefinition form of override shown above.