diff --git a/core/modules/system/templates/menu.html.twig b/core/modules/system/templates/menu.html.twig
index 03704f2..6eaafe0 100644
--- a/core/modules/system/templates/menu.html.twig
+++ b/core/modules/system/templates/menu.html.twig
@@ -29,6 +29,11 @@
 {{ menus.menu_links(items, attributes, 0) }}
 
 {% macro menu_links(items, attributes, menu_level) %}
+  {#
+    This macro can only access the variables passed to it in its arguments. To
+    access additional variables, add more arguments to this macro; or see
+    http://twig.sensiolabs.org/doc/tags/macro.html
+  #}
   {% import _self as menus %}
   {% if items %}
     {% if menu_level == 0 %}
diff --git a/core/themes/classy/templates/navigation/menu.html.twig b/core/themes/classy/templates/navigation/menu.html.twig
index e482ef4..a08353f 100644
--- a/core/themes/classy/templates/navigation/menu.html.twig
+++ b/core/themes/classy/templates/navigation/menu.html.twig
@@ -27,6 +27,11 @@
 {{ menus.menu_links(items, attributes, 0) }}
 
 {% macro menu_links(items, attributes, menu_level) %}
+  {#
+    This macro can only access the variables passed to it in its arguments. To
+    access additional variables, add more arguments to this macro; or see
+    http://twig.sensiolabs.org/doc/tags/macro.html
+  #}
   {% import _self as menus %}
   {% if items %}
     {% if menu_level == 0 %}
diff --git a/core/themes/stable/templates/navigation/menu.html.twig b/core/themes/stable/templates/navigation/menu.html.twig
index 33efca8..3b5c46d 100644
--- a/core/themes/stable/templates/navigation/menu.html.twig
+++ b/core/themes/stable/templates/navigation/menu.html.twig
@@ -27,6 +27,11 @@
 {{ menus.menu_links(items, attributes, 0) }}
 
 {% macro menu_links(items, attributes, menu_level) %}
+  {#
+    This macro can only access the variables passed to it in its arguments. To
+    access additional variables, add more arguments to this macro; or see
+    http://twig.sensiolabs.org/doc/tags/macro.html
+  #}
   {% import _self as menus %}
   {% if items %}
     {% if menu_level == 0 %}