diff --git a/core/themes/classy/templates/layout/page.html.twig b/core/themes/classy/templates/layout/page.html.twig
index 7accceb..94c90a5 100644
--- a/core/themes/classy/templates/layout/page.html.twig
+++ b/core/themes/classy/templates/layout/page.html.twig
@@ -41,6 +41,8 @@
  *   comment/reply/12345).
  *
  * Regions:
+ * - page.header_first: Items for the first header region.
+ * - page.header_second: Items for the second header region.
  * - page.header: Items for the header region.
  * - page.messages: Status and error messages. Should be displayed prominently.
  * - page.primary_menu: Items for the primary menu region.