diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index afbb6c35e3..79a5602850 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -9401,6 +9401,7 @@ SET XML OPTION { DOCUMENT | CONTENT };
         double quotes if you need to include whitespace or commas in the name.
         This parameter can only be set at server start.  If a specified
         library is not found, the server will fail to start.
+        Libraries are loaded in the order in which they appear in the list.
        </para>
 
        <para>
diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index bd01ec0526..7251b88ad1 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -261,8 +261,11 @@ static int	common_prefix_cmp(const void *a, const void *b);
  * after the standard planning process.  The plugin would normally call
  * standard_planner().
  *
- * Note to plugin authors: standard_planner() scribbles on its Query input,
- * so you'd better copy that data structure if you want to plan more than once.
+ * Notes to plugin authors:
+ * 1. standard_planner() scribbles on its Query input, so you'd better copy that
+ * data structure if you want to plan more than once.
+ * 2. If your extension implements some planning activity, write in the extension
+ * docs a requirement to set the extension at the begining of shared libraries list.
  *
  *****************************************************************************/
 PlannedStmt *