diff --git a/src/backend/optimizer/path/joinpath.c b/src/backend/optimizer/path/joinpath.c
index 821d282497..b2916ad690 100644
--- a/src/backend/optimizer/path/joinpath.c
+++ b/src/backend/optimizer/path/joinpath.c
@@ -333,7 +333,10 @@ add_paths_to_joinrel(PlannerInfo *root,
 												 jointype, &extra);
 
 	/*
-	 * 6. Finally, give extensions a chance to manipulate the path list.
+	 * 6. Finally, give extensions a chance to manipulate the path list.  They
+	 * could add new paths (such as CustomPaths) by calling add_path(), or
+	 * add_partial_path() if parallel aware.  They could also delete or modify
+	 * paths added by the core code.
 	 */
 	if (set_join_pathlist_hook)
 		set_join_pathlist_hook(root, joinrel, outerrel, innerrel,