-;;; Compute the effective slots of class, copying inherited slots and
-;;; side-effecting direct slots.
+;;; Compute the effective slots of CLASS, copying inherited slots and
+;;; destructively modifying direct slots.
+;;;
+;;; FIXME: It'd be nice to explain why it's OK to destructively modify
+;;; direct slots. Presumably it follows from the semantics of
+;;; inheritance and redefinition of conditions, but finding the cite
+;;; and documenting it here would be good. (Or, if this is not in fact
+;;; ANSI-compliant, fixing it would also be good.:-)