diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index 646e428e8b883e11202b79b9905c76e48f0a8fa6..9b89250fc950617f253f62273265ea3d8f4370de 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -596,7 +596,7 @@ function template_preprocess_datetime_wrapper(&$variables) {
  *
  * Unfortunately links templates duplicate the "active" class handling of l()
  * and LinkGenerator::generate() because it needs to be able to set the "active"
- * class not on the links themselves ("a" tags), but on the list items ("li"
+ * class not on the links themselves (<a> tags), but on the list items (<li>
  * tags) that contain the links. This is necessary for CSS to be able to style
  * list items differently when the link is active, since CSS does not yet allow
  * one to style list items only if it contains a certain element with a certain
@@ -656,7 +656,7 @@ function template_preprocess_links(&$variables) {
   if (!empty($links)) {
     // Prepend the heading to the list, if any.
     if (!empty($heading)) {
-      // Convert a string heading into an array, using a H2 tag by default.
+      // Convert a string heading into an array, using a <h2> tag by default.
       if (is_string($heading)) {
         $heading = array('text' => $heading);
       }
@@ -858,28 +858,28 @@ function template_preprocess_image(&$variables) {
  *   - colgroups: An array of column groups. Each element of the array can be
  *     either:
  *     - An array of columns, each of which is an associative array of HTML
- *       attributes applied to the COL element.
- *     - An array of attributes applied to the COLGROUP element, which must
- *       include a "data" attribute. To add attributes to COL elements, set the
- *       "data" attribute with an array of columns, each of which is an
+ *       attributes applied to the <col> element.
+ *     - An array of attributes applied to the <colgroup> element, which must
+ *       include a "data" attribute. To add attributes to <col> elements,
+ *       set the "data" attribute with an array of columns, each of which is an
  *       associative array of HTML attributes.
  *     Here's an example for $colgroup:
  *     @code
  *     $colgroup = array(
- *       // COLGROUP with one COL element.
+ *       // <colgroup> with one <col> element.
  *       array(
  *         array(
- *           'class' => array('funky'), // Attribute for the COL element.
+ *           'class' => array('funky'), // Attribute for the <col> element.
  *         ),
  *       ),
- *       // Colgroup with attributes and inner COL elements.
+ *       // <colgroup> with attributes and inner <col> elements.
  *       array(
  *         'data' => array(
  *           array(
- *             'class' => array('funky'), // Attribute for the COL element.
+ *             'class' => array('funky'), // Attribute for the <col> element.
  *           ),
  *         ),
- *         'class' => array('jazzy'), // Attribute for the COLGROUP element.
+ *         'class' => array('jazzy'), // Attribute for the <colgroup> element.
  *       ),
  *     );
  *     @endcode
@@ -1157,7 +1157,7 @@ function template_preprocess_container(&$variables) {
  *   An associative array containing:
  *   - items: An associative array of maintenance tasks.
  *     It's the caller's responsibility to ensure this array's items contain no
- *     dangerous HTML such as SCRIPT tags.
+ *     dangerous HTML such as <script> tags.
  *   - active: The key for the currently active maintenance task.
  */
 function template_preprocess_maintenance_task_list(&$variables) {
@@ -1267,7 +1267,7 @@ function template_preprocess_html(&$variables) {
 
   $variables['html_attributes'] = new Attribute();
 
-  // HTML element attributes.
+  // <html> element attributes.
   $language_interface = \Drupal::languageManager()->getCurrentLanguage();
   $variables['html_attributes']['lang'] = $language_interface->getId();
   $variables['html_attributes']['dir'] = $language_interface->getDirection();
diff --git a/core/misc/ajax.js b/core/misc/ajax.js
index 061b5947cc278a7153a9c0c57517ba12e995989a..fefe9f3031efa4b10243d83a087a7fe06bb833e6 100644
--- a/core/misc/ajax.js
+++ b/core/misc/ajax.js
@@ -1035,11 +1035,11 @@
       // been sufficiently tested whether attachBehaviors() can be successfully
       // called with a context object that includes top-level text nodes.
       // However, to give developers full control of the HTML appearing in the
-      // page, and to enable Ajax content to be inserted in places where DIV
-      // elements are not allowed (e.g., within TABLE, TR, and SPAN parents),
-      // we check if the new content satisfies the requirement of a single
-      // top-level element, and only use the container DIV created above when
-      // it doesn't. For more information, please see
+      // page, and to enable Ajax content to be inserted in places where <div>
+      // elements are not allowed (e.g., within <table>, <tr>, and <span>
+      // parents), we check if the new content satisfies the requirement
+      // of a single top-level element, and only use the container <div> created
+      // above when it doesn't. For more information, please see
       // https://www.drupal.org/node/736066.
       if ($new_content.length !== 1 || $new_content.get(0).nodeType !== 1) {
         $new_content = $new_content_wrapped;
diff --git a/core/misc/tableselect.js b/core/misc/tableselect.js
index 053af05d9bcbc1f891a340ec3ad5e2324966ad49..243e0001107d29a8d9e4c0e21bc250da2cb8c692 100644
--- a/core/misc/tableselect.js
+++ b/core/misc/tableselect.js
@@ -101,7 +101,7 @@
       // range. Also make sure that we are actually checking checkboxes
       // over a range and that a checkbox has been checked or unchecked before.
       if (e.shiftKey && lastChecked && lastChecked !== e.target) {
-        // We use the checkbox's parent TR to do our range searching.
+        // We use the checkbox's parent <tr> to do our range searching.
         Drupal.tableSelectRange($(e.target).closest('tr')[0], $(lastChecked).closest('tr')[0], e.target.checked);
       }
 
diff --git a/core/modules/field_ui/templates/field-ui-table.html.twig b/core/modules/field_ui/templates/field-ui-table.html.twig
index f7ff02681b7667aab82758310110f46159e1e2f6..68c8c8ec92ffa9b6b4d969259c32c9550794f6a8 100644
--- a/core/modules/field_ui/templates/field-ui-table.html.twig
+++ b/core/modules/field_ui/templates/field-ui-table.html.twig
@@ -24,7 +24,7 @@
  *   - no_striping: A flag indicating that the row should receive no
  *     'even / odd' styling. Defaults to FALSE.
  *   - cells: Table cells of the row. Each cell contains the following keys:
- *     - tag: The HTML tag name to use; either TH or TD.
+ *     - tag: The HTML tag name to use; either 'th' or 'td'.
  *     - attributes: Any HTML attributes, such as "colspan", to apply to the
  *       table cell.
  *     - content: The string to display in the table cell.
diff --git a/core/modules/system/templates/fieldset.html.twig b/core/modules/system/templates/fieldset.html.twig
index b67ec85f3cdc040c5276cbb155d9501c1d1a6a83..bacd1d4d138b86762c9abeb603c39b39ce38e625 100644
--- a/core/modules/system/templates/fieldset.html.twig
+++ b/core/modules/system/templates/fieldset.html.twig
@@ -4,18 +4,19 @@
  * Default theme implementation for a fieldset element and its children.
  *
  * Available variables:
- * - attributes: HTML attributes for the fieldset element.
- * - errors: (optional) Any errors for this fieldset element, may not be set.
- * - required: Boolean indicating whether the fieldeset element is required.
- * - legend: The legend element containing the following properties:
- *   - title: Title of the fieldset, intended for use as the text of the legend.
- *   - attributes: HTML attributes to apply to the legend.
+ * - attributes: HTML attributes for the <fieldset> element.
+ * - errors: (optional) Any errors for this <fieldset> element, may not be set.
+ * - required: Boolean indicating whether the <fieldeset> element is required.
+ * - legend: The <legend> element containing the following properties:
+ *   - title: Title of the <fieldset>, intended for use as the text
+       of the <legend>.
+ *   - attributes: HTML attributes to apply to the <legend> element.
  * - description: The description element containing the following properties:
- *   - content: The description content of the fieldset.
+ *   - content: The description content of the <fieldset>.
  *   - attributes: HTML attributes to apply to the description container.
- * - children: The rendered child elements of the fieldset.
- * - prefix: The content to add before the fieldset children.
- * - suffix: The content to add after the fieldset children.
+ * - children: The rendered child elements of the <fieldset>.
+ * - prefix: The content to add before the <fieldset> children.
+ * - suffix: The content to add after the <fieldset> children.
  *
  * @see template_preprocess_fieldset()
  *
@@ -38,7 +39,7 @@
       required ? 'form-required',
     ]
   %}
-  {#  Always wrap fieldset legends in a SPAN for CSS positioning. #}
+  {#  Always wrap fieldset legends in a <span> for CSS positioning. #}
   <legend{{ legend.attributes }}>
     <span{{ legend_span.attributes.addClass(legend_span_classes) }}>{{ legend.title }}</span>
   </legend>
diff --git a/core/modules/system/templates/region.html.twig b/core/modules/system/templates/region.html.twig
index e009455065be932891b37fa091930e47fe3a43e9..219e14b0a4bef8bbac01f586f227a2daa4c97525 100644
--- a/core/modules/system/templates/region.html.twig
+++ b/core/modules/system/templates/region.html.twig
@@ -5,7 +5,7 @@
  *
  * Available variables:
  * - content: The content for this region, typically blocks.
- * - attributes: HTML attributes for the region div.
+ * - attributes: HTML attributes for the region <div>.
  * - region: The name of the region variable as defined in the theme's
  *   .info.yml file.
  *
diff --git a/core/modules/system/templates/select.html.twig b/core/modules/system/templates/select.html.twig
index fb7226e77081072fe839336bee43e275984c8b26..0b5c3d22c58dfeeacd0d1c150878ab9a02dc23e6 100644
--- a/core/modules/system/templates/select.html.twig
+++ b/core/modules/system/templates/select.html.twig
@@ -4,8 +4,8 @@
  * Default theme implementation for a select element.
  *
  * Available variables:
- * - attributes: HTML attributes for the select tag.
- * - options: The option element children.
+ * - attributes: HTML attributes for the <select> tag.
+ * - options: The <option> element children.
  *
  * @see template_preprocess_select()
  *
diff --git a/core/modules/system/templates/table.html.twig b/core/modules/system/templates/table.html.twig
index f6b32e4753e8bde2e646d806b7e33ac7834232e9..443657014f61b230df6709a88f771232e9d61aa8 100644
--- a/core/modules/system/templates/table.html.twig
+++ b/core/modules/system/templates/table.html.twig
@@ -12,7 +12,7 @@
  *     https://www.drupal.org/node/893530 and
  *     http://api.drupal.org/api/drupal/includes!theme.inc/function/theme_table/7#comment-5109.
  * - header: Table header cells. Each cell contains the following properties:
- *   - tag: The HTML tag name to use; either TH or TD.
+ *   - tag: The HTML tag name to use; either 'th' or 'td'.
  *   - attributes: HTML attributes to apply to the tag.
  *   - content: A localized string for the title of the column.
  *   - field: Field name (required for column sorting).
@@ -24,7 +24,7 @@
  *   - no_striping: A flag indicating that the row should receive no
  *     'even / odd' styling. Defaults to FALSE.
  *   - cells: Table cells of the row. Each cell contains the following keys:
- *     - tag: The HTML tag name to use; either TH or TD.
+ *     - tag: The HTML tag name to use; either 'th' or 'td'.
  *     - attributes: Any HTML attributes, such as "colspan", to apply to the
  *       table cell.
  *     - content: The string to display in the table cell.
diff --git a/core/modules/system/templates/textarea.html.twig b/core/modules/system/templates/textarea.html.twig
index 6a1a46efeda76a19a9e63e54725d51070542f4ab..cd987d2f937b59fe8c673eb01146c46e9ceb1c02 100644
--- a/core/modules/system/templates/textarea.html.twig
+++ b/core/modules/system/templates/textarea.html.twig
@@ -5,7 +5,7 @@
  *
  * Available variables
  * - wrapper_attributes: A list of HTML attributes for the wrapper element.
- * - attributes: A list of HTML attributes for the textarea element.
+ * - attributes: A list of HTML attributes for the <textarea> element.
  * - resizable: An indicator for whether the textarea is resizable.
  * - required: An indicator for whether the textarea is required.
  * - value: The textarea content.
diff --git a/core/themes/classy/templates/dataset/table.html.twig b/core/themes/classy/templates/dataset/table.html.twig
index 70801d61b18db503cc7068c31242e39a65b7e7b8..2afa9c155642349eea89066b17ad245044558b80 100644
--- a/core/themes/classy/templates/dataset/table.html.twig
+++ b/core/themes/classy/templates/dataset/table.html.twig
@@ -12,7 +12,7 @@
  *     https://www.drupal.org/node/893530 and
  *     http://api.drupal.org/api/drupal/includes!theme.inc/function/theme_table/7#comment-5109.
  * - header: Table header cells. Each cell contains the following properties:
- *   - tag: The HTML tag name to use; either TH or TD.
+ *   - tag: The HTML tag name to use; either 'th' or 'td'.
  *   - attributes: HTML attributes to apply to the tag.
  *   - content: A localized string for the title of the column.
  *   - field: Field name (required for column sorting).
@@ -24,7 +24,7 @@
  *   - no_striping: A flag indicating that the row should receive no
  *     'even / odd' styling. Defaults to FALSE.
  *   - cells: Table cells of the row. Each cell contains the following keys:
- *     - tag: The HTML tag name to use; either TH or TD.
+ *     - tag: The HTML tag name to use; either 'th' or 'td'.
  *     - attributes: Any HTML attributes, such as "colspan", to apply to the
  *       table cell.
  *     - content: The string to display in the table cell.
diff --git a/core/themes/classy/templates/form/fieldset.html.twig b/core/themes/classy/templates/form/fieldset.html.twig
index 4bd7d0a62aca53a0179c396caa1940a00e07ef27..0d089ed3813dd791faf6107a0e3b21b53245119a 100644
--- a/core/themes/classy/templates/form/fieldset.html.twig
+++ b/core/themes/classy/templates/form/fieldset.html.twig
@@ -36,7 +36,7 @@
       required ? 'form-required',
     ]
   %}
-  {#  Always wrap fieldset legends in a SPAN for CSS positioning. #}
+  {#  Always wrap fieldset legends in a <span> for CSS positioning. #}
   <legend{{ legend.attributes }}>
     <span{{ legend_span.attributes.addClass(legend_span_classes) }}>{{ legend.title }}</span>
   </legend>
diff --git a/core/themes/classy/templates/form/select.html.twig b/core/themes/classy/templates/form/select.html.twig
index 3150bdcb36e3af4fcaa85e5ac53b9f97796d9b7f..8af42616f74a825190651a95557231b56dce3794 100644
--- a/core/themes/classy/templates/form/select.html.twig
+++ b/core/themes/classy/templates/form/select.html.twig
@@ -4,8 +4,8 @@
  * Theme override for a select element.
  *
  * Available variables:
- * - attributes: HTML attributes for the select tag.
- * - options: The option element children.
+ * - attributes: HTML attributes for the <select> tag.
+ * - options: The <option> element children.
  *
  * @see template_preprocess_select()
  */
diff --git a/core/themes/classy/templates/form/textarea.html.twig b/core/themes/classy/templates/form/textarea.html.twig
index 24e647b78e9c6ad60943d3a715aeff69af0ea01c..99e1bde09059aa3424260dcc53cefb2113288ecb 100644
--- a/core/themes/classy/templates/form/textarea.html.twig
+++ b/core/themes/classy/templates/form/textarea.html.twig
@@ -5,7 +5,7 @@
  *
  * Available variables
  * - wrapper_attributes: A list of HTML attributes for the wrapper element.
- * - attributes: A list of HTML attributes for the textarea element.
+ * - attributes: A list of HTML attributes for the <textarea> element.
  * - resizable: An indicator for whether the textarea is resizable.
  * - required: An indicator for whether the textarea is required.
  * - value: The textarea content.
diff --git a/core/themes/classy/templates/layout/region.html.twig b/core/themes/classy/templates/layout/region.html.twig
index cff654ab59ac695c7c3e84de360094ae01ac3fe5..95e71cec37e409bdfab1d8d90e0a192bede54e9c 100644
--- a/core/themes/classy/templates/layout/region.html.twig
+++ b/core/themes/classy/templates/layout/region.html.twig
@@ -5,7 +5,7 @@
  *
  * Available variables:
  * - content: The content for this region, typically blocks.
- * - attributes: HTML attributes for the region div.
+ * - attributes: HTML attributes for the region <div>.
  * - region: The name of the region variable as defined in the theme's
  *   .info.yml file.
  *
diff --git a/core/themes/seven/css/components/tables.css b/core/themes/seven/css/components/tables.css
index 3bdf7cc63bab3615181de0126090ec03aeb0798f..913e21a42c2fbe343eb0c0429a91fafae689c10e 100644
--- a/core/themes/seven/css/components/tables.css
+++ b/core/themes/seven/css/components/tables.css
@@ -116,7 +116,7 @@ td.is-active {
   background: none;
 }
 
-/* Force browsers to calculate the width of a 'select all' TH element. */
+/* Force browsers to calculate the width of a 'select all' <th> element. */
 th.select-all {
   width: 1px;
 }
diff --git a/core/themes/stable/templates/admin/field-ui-table.html.twig b/core/themes/stable/templates/admin/field-ui-table.html.twig
index 5a058520f5d611c0b77c0e45e42531b5ff71ba40..72523f60fd7c06f4abfc21ef7a1b5aff6733ae6a 100644
--- a/core/themes/stable/templates/admin/field-ui-table.html.twig
+++ b/core/themes/stable/templates/admin/field-ui-table.html.twig
@@ -12,7 +12,7 @@
  *     https://www.drupal.org/node/893530 and
  *     http://api.drupal.org/api/drupal/includes!theme.inc/function/theme_table/7#comment-5109.
  * - header: Table header cells. Each cell contains the following properties:
- *   - tag: The HTML tag name to use; either TH or TD.
+ *   - tag: The HTML tag name to use; either 'th' or 'td'.
  *   - attributes: HTML attributes to apply to the tag.
  *   - content: A localized string for the title of the column.
  *   - field: Field name (required for column sorting).
@@ -24,7 +24,7 @@
  *   - no_striping: A flag indicating that the row should receive no
  *     'even / odd' styling. Defaults to FALSE.
  *   - cells: Table cells of the row. Each cell contains the following keys:
- *     - tag: The HTML tag name to use; either TH or TD.
+ *     - tag: The HTML tag name to use; either 'th' or 'td'.
  *     - attributes: Any HTML attributes, such as "colspan", to apply to the
  *       table cell.
  *     - content: The string to display in the table cell.
diff --git a/core/themes/stable/templates/dataset/table.html.twig b/core/themes/stable/templates/dataset/table.html.twig
index b7267be5cfe58aa4f843f371988755e9907197e9..231ada2b38b8281eb6a31a0a08588fef69aa2063 100644
--- a/core/themes/stable/templates/dataset/table.html.twig
+++ b/core/themes/stable/templates/dataset/table.html.twig
@@ -12,7 +12,7 @@
  *     https://www.drupal.org/node/893530 and
  *     http://api.drupal.org/api/drupal/includes!theme.inc/function/theme_table/7#comment-5109.
  * - header: Table header cells. Each cell contains the following properties:
- *   - tag: The HTML tag name to use; either TH or TD.
+ *   - tag: The HTML tag name to use; either 'th' or 'td'.
  *   - attributes: HTML attributes to apply to the tag.
  *   - content: A localized string for the title of the column.
  *   - field: Field name (required for column sorting).
@@ -24,7 +24,7 @@
  *   - no_striping: A flag indicating that the row should receive no
  *     'even / odd' styling. Defaults to FALSE.
  *   - cells: Table cells of the row. Each cell contains the following keys:
- *     - tag: The HTML tag name to use; either TH or TD.
+ *     - tag: The HTML tag name to use; either 'th' or 'td'.
  *     - attributes: Any HTML attributes, such as "colspan", to apply to the
  *       table cell.
  *     - content: The string to display in the table cell.