diff --git a/core/modules/system/templates/region.html.twig b/core/modules/system/templates/region.html.twig
index 3be79cc..14f0c6a 100644
--- a/core/modules/system/templates/region.html.twig
+++ b/core/modules/system/templates/region.html.twig
@@ -6,7 +6,13 @@
  * Available variables:
  * - content: The content for this region, typically blocks.
  * - attributes: HTML attributes.
- * - attributes.class: String of classes that can be used to style contextually through CSS.
+ *  - attributes.class: String of classes that can be used to style
+ *    contextually through CSS.
+ *    - region: The current template type (also know as "theming hook").
+ *    - region-[name]: The name of the region with underscores replaced with
+ *      dashes. For example, page_top region would have a region-page-top class.
+ * - region: The name of the region variable as defined in the theme's
+ *   .info.yml file.
  *
  * @see template_preprocess()
  * @see template_preprocess_region()