diff --git a/core/modules/block/templates/block.html.twig b/core/modules/block/templates/block.html.twig
index 2680121..2c3cae8 100644
--- a/core/modules/block/templates/block.html.twig
+++ b/core/modules/block/templates/block.html.twig
@@ -19,10 +19,15 @@
  *   - 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: String of RDFa attributes populated by modules, intended to
+ *   be added to the main container tag of this template. This is either an
+ *   empty string or a string containing a leading space, so it should be
+ *   printed without a leading space before what precedes it.
  *   - 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/modules/comment/templates/comment.html.twig b/core/modules/comment/templates/comment.html.twig
index 575510f..07dce6e 100644
--- a/core/modules/comment/templates/comment.html.twig
+++ b/core/modules/comment/templates/comment.html.twig
@@ -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  *   - node--unpublished: Appears on unpublished nodes visible only to site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