--- modules/system/system.api.php	2015-08-19 23:20:31.000000000 +0200
+++ modules/system/system.api.php	2016-07-07 20:25:52.000000000 +0200
@@ -3189,7 +3205,9 @@
  * creation and alteration of the supported database engines.
  *
  * See the Schema API Handbook at http://drupal.org/node/146843 for details on
- * schema definition structures.
+ * schema definition structures. Note that foreign key definitions are for
+ * documentation purposes only; foreign keys are not created in the database,
+ * nor are they enforced by Drupal.
  *
  * @return array
  *   A schema definition structure array. For each element of the