-;;; Otherwise, it calls %WITH-ARRAY-DATA. Note that there is a
-;;; DERIVE-TYPE method for %WITH-ARRAY-DATA.
+;;; Otherwise, it calls %WITH-ARRAY-DATA. Note that %WITH-ARRAY-DATA
+;;; may be further optimized.
+;;;
+;;; Given any ARRAY, bind DATA-VAR to the array's data vector and
+;;; START-VAR and END-VAR to the start and end of the designated
+;;; portion of the data vector. SVALUE and EVALUE are any start and
+;;; end specified to the original operation, and are factored into the
+;;; bindings of START-VAR and END-VAR. OFFSET-VAR is the cumulative
+;;; offset of all displacements encountered, and does not include
+;;; SVALUE.