diff --git a/core/modules/block/templates/block.html.twig b/core/modules/block/templates/block.html.twig
index 2680121..aa750cb 100644
--- a/core/modules/block/templates/block.html.twig
+++ b/core/modules/block/templates/block.html.twig
@@ -19,10 +19,11 @@
  *   - delta: An ID for the block, unique within each module.
  *   - region: The block region embedding the current block.
  * - content: The content of this block.
- * - attributes: HTML attributes for the containing element.
+ * - attributes: array of HTML attributes populated by modules, intended to
+ *   be added to the main container tag of this template.
  *   - id: A valid HTML ID and guaranteed unique.
- * - title_attributes: HTML attributes for the title element.
- * - content_attributes: HTML attributes for the content element.
+ * - title_attributes: Same as attributes, except applied to the main title
+ *   tag that appears in the template.
  * - title_prefix: Additional output populated by modules, intended to be
  *   displayed in front of the main title tag that appears in the template.
  * - title_suffix: Additional output populated by modules, intended to be
diff --git a/core/modules/comment/templates/comment.html.twig b/core/modules/comment/templates/comment.html.twig
index 575510f..35c88e9 100644
--- a/core/modules/comment/templates/comment.html.twig
+++ b/core/modules/comment/templates/comment.html.twig
@@ -26,8 +26,8 @@
  * - status: Comment status. Possible values are:
  *   unpublished, published, or preview.
  * - title: Comment title, linked to the comment.
- * - attributes.class: List of classes that can be used to style contextually
- *   through CSS. The default values can be one or more of the following:
+ * - attributes: HTML attributes for the containing element.
+ *   The attributes.class may contain one or more of the following classes:
  *   - comment: The current template type; e.g., 'theming hook'.
  *   - by-anonymous: Comment by an unregistered user.
  *   - by-{entity-type}-author: Comment by the author of the parent entity,
@@ -40,6 +40,8 @@
  * - title_suffix: Additional output populated by modules, intended to be
  *   displayed after the main title tag that appears in the template.
  * - content_attributes: List of classes for the styling of the comment content.
+ * - title_attributes: Same as attributes, except applied to the main title
+ *   tag that appears in the template.
  *
  * These variables are provided to give context about the parent comment (if
  * any):
diff --git a/core/modules/node/templates/node.html.twig b/core/modules/node/templates/node.html.twig
index 37f1bfc..c08ab7c 100644
--- a/core/modules/node/templates/node.html.twig
+++ b/core/modules/node/templates/node.html.twig
@@ -39,6 +39,12 @@
  *     teaser listings.
  *   - node--unpublished: Appears on unpublished nodes visible only to site
  *     admins.
+ * - title_attributes: Same as attributes, except applied to the main title
+ *   tag that appears in the template.
+ * - content_attributes: Same as attributes, except applied to the main
+ *   content tag that appears in the template.
+ * - author_attributes: Same as attributes, except applied to the author of
+ *   the node tag that appears in the template.
  * - title_prefix: Additional output populated by modules, intended to be
  *   displayed in front of the main title tag that appears in the template.
  * - title_suffix: Additional output populated by modules, intended to be
diff --git a/core/themes/bartik/templates/block.html.twig b/core/themes/bartik/templates/block.html.twig
index 7883a09..31a95c0 100644
--- a/core/themes/bartik/templates/block.html.twig
+++ b/core/themes/bartik/templates/block.html.twig
@@ -19,10 +19,13 @@
  *   - delta: An ID for the block, unique within each module.
  *   - region: The block region embedding the current block.
  * - content: The content of this block.
- * - attributes: HTML attributes for the containing element.
+ * - attributes: array of HTML attributes populated by modules, intended to
+ *   be added to the main container tag of this template.
  *   - id: A valid HTML ID and guaranteed unique.
- * - title_attributes: HTML attributes for the title element.
- * - content_attributes: HTML attributes for the content element.
+ * - title_attributes: Same as attributes, except applied to the main title
+ *   tag that appears in the template.
+ * - content_attributes: Same as attributes, except applied to the main content
+ *   tag that appears in the template.
  * - title_prefix: Additional output populated by modules, intended to be
  *   displayed in front of the main title tag that appears in the template.
  * - title_suffix: Additional output populated by modules, intended to be
diff --git a/core/themes/bartik/templates/comment.html.twig b/core/themes/bartik/templates/comment.html.twig
index 7a22fc0..c5c0a7a 100644
--- a/core/themes/bartik/templates/comment.html.twig
+++ b/core/themes/bartik/templates/comment.html.twig
@@ -26,8 +26,8 @@
  * - status: Comment status. Possible values are:
  *   unpublished, published, or preview.
  * - title: Comment title, linked to the comment.
- * - attributes.class: List of classes that can be used to style contextually
- *   through CSS. The default values can be one or more of the following:
+ * - attributes: HTML attributes for the containing element.
+ *   The attributes.class may contain one or more of the following classes:
  *   - comment: The current template type; e.g., 'theming hook'.
  *   - by-anonymous: Comment by an unregistered user.
  *   - by-{entity-type}-author: Comment by the author of the parent entity,
@@ -39,6 +39,8 @@
  *   displayed in front of the main title tag that appears in the template.
  * - title_suffix: Additional output populated by modules, intended to be
  *   displayed after the main title tag that appears in the template.
+ * - title_attributes: Same as attributes, except applied to the main title
+ *   tag that appears in the template.
  * - content_attributes: List of classes for the styling of the comment content.
  *
  * These variables are provided to give context about the parent comment (if
diff --git a/core/themes/bartik/templates/node.html.twig b/core/themes/bartik/templates/node.html.twig
index c4eddea..3150206 100644
--- a/core/themes/bartik/templates/node.html.twig
+++ b/core/themes/bartik/templates/node.html.twig
@@ -39,6 +39,12 @@
  *     teaser listings.
  *   - node--unpublished: Appears on unpublished nodes visible only to site
  *     admins.
+ * - title_attributes: Same as attributes, except applied to the main title
+ *   tag that appears in the template.
+ * - content_attributes: Same as attributes, except applied to the main
+ *   content tag that appears in the template.
+ * - author_attributes: Same as attributes, except applied to the author of
+ *   the node tag that appears in the template.
  * - title_prefix: Additional output populated by modules, intended to be
  *   displayed in front of the main title tag that appears in the template.
  * - title_suffix: Additional output populated by modules, intended to be