Index: src/vdbe.c
==================================================================
--- src/vdbe.c
+++ src/vdbe.c
@@ -5036,10 +5036,17 @@
 ** This flag avoids doing an extra seek.
 **
 ** This instruction only works for indices.  The equivalent instruction
 ** for tables is OP_Insert.
 */
+/* Opcode: SorterInsert P1 P2 * * *
+** Synopsis: key=r[P2]
+**
+** Register P2 holds an SQL index key made using the
+** MakeRecord instructions.  This opcode writes that key
+** into the sorter P1.  Data for the entry is nil.
+*/
 case OP_SorterInsert:       /* in2 */
 case OP_IdxInsert: {        /* in2 */
   VdbeCursor *pC;
   BtreePayload x;