1 files changed, 3 insertions, 0 deletions
diff --git a/Include/listobject.h b/Include/listobject.h
index 62a8518..ffce029 100644
--- a/Include/listobject.h
+++ b/Include/listobject.h
@@ -30,6 +30,9 @@ typedef struct {
      *     0 <= ob_size <= allocated
      *     len(list) == ob_size
      *     ob_item == NULL implies ob_size == allocated == 0
+     *     If ob_item ever becomes non-NULL, it remains non-NULL for the
+     *         life of the list object.  The check for mutation in list.sort()
+     *         relies on this odd detail.
      */
     int allocated;
 } PyListObject;