diff --git a/core/includes/ajax.inc b/core/includes/ajax.inc
index 7ab2059..b72bb01 100644
--- a/core/includes/ajax.inc
+++ b/core/includes/ajax.inc
@@ -111,17 +111,13 @@
  * clicked (or changed, depending on the kind of field). #ajax supports
  * the following parameters (either 'path' or 'callback' is required at least):
  * - #ajax['callback']: The callback to invoke to handle the server side of the
- *   Ajax event, which will receive a $form and $form_state as arguments, and
- *   returns a renderable array (most often a form or form fragment), an HTML
- *   string, or an array of Ajax commands. If returning a renderable array or
- *   a string, the value will replace the original element named in
- *   #ajax['wrapper'], and
- *   theme_status_messages()
- *   will be prepended to that
- *   element. (If the status messages are not wanted, return an array
- *   of Ajax commands instead.)
- *   #ajax['wrapper']. If an array of Ajax commands is returned, it will be
- *   executed by the calling code.
+ *   Ajax event. The function will be passed parameters $form and $form_state,
+ *   and should return either a renderable array (most often a form or form
+ *   fragment), an HTML string, or an array of Ajax commands. If you return a
+ *   renderable array or a string, the value will replace the original element
+ *   named in #ajax['wrapper'], and the output of status-messages.html.twig
+ *   will be prepended to that element. If you return an array of Ajax commands,
+ *   they will be executed by the calling code.
  * - #ajax['path']: The menu path to use for the request. This is often omitted
  *   and the default is used. This path should map
  *   to a controller that returns data using
diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index 83aa307..9a71c86 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -1262,7 +1262,7 @@ function watchdog($type, $message, array $variables = NULL, $severity = WATCHDOG
  *   Or, if there are no messages set, the function returns NULL.
  *
  * @see drupal_get_messages()
- * @see theme_status_messages()
+ * @see status-messages.html.twig
  */
 function drupal_set_message($message = NULL, $type = 'status', $repeat = FALSE) {
   if ($message) {
@@ -1305,7 +1305,7 @@ function drupal_set_message($message = NULL, $type = 'status', $repeat = FALSE)
  *   is returned.
  *
  * @see drupal_set_message()
- * @see theme_status_messages()
+ * @see status-messages.html.twig
  */
 function drupal_get_messages($type = NULL, $clear_queue = TRUE) {
   if ($messages = drupal_set_message()) {
diff --git a/core/includes/form.inc b/core/includes/form.inc
index 1c6af1b..de51894 100644
--- a/core/includes/form.inc
+++ b/core/includes/form.inc
@@ -1471,7 +1471,7 @@ function form_pre_render_actions_dropbutton(array $element) {
         );
       }
       // Add this button to the corresponding dropbutton.
-      // @todo Change #type 'dropbutton' to be based on theme_item_list()
+      // @todo Change #type 'dropbutton' to be based on item-list.html.twig
       //   instead of links.html.twig to avoid this preemptive rendering.
       $button = drupal_render($element[$key]);
       $dropbuttons[$dropbutton]['#links'][$key] = array(
@@ -2930,7 +2930,7 @@ function theme_form_required_marker($variables) {
  *
  * Form element labels include the #title and a #required marker. The label is
  * associated with the element itself by the element #id. Labels may appear
- * before or after elements, depending on theme_form_element() and
+ * before or after elements, depending on form-element.html.twig and
  * #title_display.
  *
  * This function will not be called for elements with no labels, depending on
diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index 8f69720..5a414eb 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -1027,7 +1027,7 @@ function theme_disable($theme_list) {
  */
 
 /**
- * Preprocess variables for theme_datetime().
+ * Preprocesses variables for datetime.html.twig.
  *
  * @param array $variables
  *   An associative array possibly containing:
@@ -1751,9 +1751,9 @@ function template_preprocess_item_list(&$variables) {
         // If this child element does not specify how it can be rendered, then
         // we need to inherit the render properties of the current list.
         if (!isset($child['#type']) && !isset($child['#theme']) && !isset($child['#markup'])) {
-          // Since theme_item_list() supports both strings and render arrays as
-          // items, the items of the nested list may have been specified as the
-          // child elements of the nested list, instead of #items. For
+          // Since item-list.html.twig supports both strings and render arrays
+          // as items, the items of the nested list may have been specified as
+          // the child elements of the nested list, instead of #items. For
           // convenience, we automatically move them into #items.
           if (!isset($child['#items'])) {
             // This is the same condition as in
@@ -2262,7 +2262,7 @@ function theme_get_suggestions($args, $base, $delimiter = '__') {
 }
 
 /**
- * Prepare variables for maintenance page templates.
+ * Prepares variables for maintenance page templates.
  *
  * Default template: maintenance-page.html.twig.
  *
diff --git a/core/lib/Drupal/Component/Utility/SortArray.php b/core/lib/Drupal/Component/Utility/SortArray.php
index a8d9f00..eee9415 100644
--- a/core/lib/Drupal/Component/Utility/SortArray.php
+++ b/core/lib/Drupal/Component/Utility/SortArray.php
@@ -77,7 +77,6 @@ public static function sortByTitleElement($a, $b) {
    *
    * Callback for uasort() within:
    * - system_modules()
-   * - theme_simpletest_test_table()
    *
    * @param array $a
    *   First item for comparison. The compared items should be associative arrays
diff --git a/core/lib/Drupal/Core/Form/FormBuilder.php b/core/lib/Drupal/Core/Form/FormBuilder.php
index d54a895..46e8874 100644
--- a/core/lib/Drupal/Core/Form/FormBuilder.php
+++ b/core/lib/Drupal/Core/Form/FormBuilder.php
@@ -777,9 +777,9 @@ public function prepareForm($form_id, &$form, &$form_state) {
     }
 
     // If no #theme has been set, automatically apply theme suggestions.
-    // theme_form() itself is in #theme_wrappers and not #theme. Therefore, the
-    // #theme function only has to care for rendering the inner form elements,
-    // not the form itself.
+    // form.html.twig itself is in #theme_wrappers and not #theme. Therefore,
+    // the #theme function only has to care for rendering the inner form
+    // elements, not the form itself.
     if (!isset($form['#theme'])) {
       $form['#theme'] = array($form_id);
       if (isset($form_state['build_info']['base_form_id'])) {
diff --git a/core/modules/aggregator/templates/aggregator-summary-items.html.twig b/core/modules/aggregator/templates/aggregator-summary-items.html.twig
index a00b8dc..c62cba0 100644
--- a/core/modules/aggregator/templates/aggregator-summary-items.html.twig
+++ b/core/modules/aggregator/templates/aggregator-summary-items.html.twig
@@ -8,7 +8,7 @@
  * Available variables:
  * - title: Title of the feed.
  * - summary_list: Unordered list of linked feed items generated through
- *   theme_item_list().
+ *   item-list.html.twig.
  * - source_url: URL to the local source.
  *
  * @see template_preprocess_aggregator_summary_items()
diff --git a/core/modules/block/templates/block-list.html.twig b/core/modules/block/templates/block-list.html.twig
index 474c654..854d3ce 100644
--- a/core/modules/block/templates/block-list.html.twig
+++ b/core/modules/block/templates/block-list.html.twig
@@ -5,7 +5,7 @@
  *
  * This template will be used when a block edit form specifies 'block_edit_form'
  * as its #theme callback.  Otherwise, by default, block add/edit forms will be
- * themed by theme_form().
+ * themed by form.html.twig.
  *
  * Available variables:
  * - form: The block add/edit form.
diff --git a/core/modules/book/book.module b/core/modules/book/book.module
index 8c52221..ca38c33 100644
--- a/core/modules/book/book.module
+++ b/core/modules/book/book.module
@@ -516,7 +516,7 @@ function template_preprocess_book_node_export_html(&$variables) {
 }
 
 /**
- * Implements template_preprocess_HOOK() for theme_book_tree().
+ * Implements template_preprocess_HOOK() for book-tree.html.twig.
  */
 function template_preprocess_book_tree(&$variables) {
   $variables['tree'] = $variables['tree']['#children'];
diff --git a/core/modules/filter/filter.module b/core/modules/filter/filter.module
index 40eda67..8e0d6aa 100644
--- a/core/modules/filter/filter.module
+++ b/core/modules/filter/filter.module
@@ -459,7 +459,7 @@ function filter_process_format($element) {
     // Do not copy this #process function to prevent form_builder() from
     // recursing infinitely.
     '#process',
-    // Description is handled by theme_text_format_wrapper().
+    // Description is handled by text-format-wrapper.html.twig.
     '#description',
     // Ensure proper ordering of children.
     '#weight',
diff --git a/core/modules/node/templates/node-edit-form.html.twig b/core/modules/node/templates/node-edit-form.html.twig
index c208cf5..0669727 100644
--- a/core/modules/node/templates/node-edit-form.html.twig
+++ b/core/modules/node/templates/node-edit-form.html.twig
@@ -5,7 +5,7 @@
  *
  * This template will be used when a node edit form specifies 'node_edit_form'
  * as its #theme callback.  Otherwise, by default, node add/edit forms will be
- * themed by theme_form().
+ * themed by form.html.twig.
  *
  * Available variables:
  * - form: The node add/edit form.
diff --git a/core/modules/rdf/rdf.module b/core/modules/rdf/rdf.module
index bf8c60e..3b6fb8a 100644
--- a/core/modules/rdf/rdf.module
+++ b/core/modules/rdf/rdf.module
@@ -543,7 +543,7 @@ function rdf_preprocess_taxonomy_term(&$variables) {
 }
 
 /**
- * Implements hook_preprocess_HOOK() for theme_image().
+ * Implements hook_preprocess_HOOK() for image.html.twig.
  */
 function rdf_preprocess_image(&$variables) {
   // Adds the RDF type for image.  We cannot use the usual entity-based mapping
diff --git a/core/modules/system/css/system.theme.css b/core/modules/system/css/system.theme.css
index b8678a3..ab13f91 100644
--- a/core/modules/system/css/system.theme.css
+++ b/core/modules/system/css/system.theme.css
@@ -14,7 +14,7 @@
 }
 
 /**
- * Markup generated by theme_tablesort_indicator().
+ * Markup generated by tablesort-indicator.html.twig.
  */
 th.active img {
   display: inline;
@@ -24,7 +24,7 @@ td.active {
 }
 
 /**
- * Markup generated by theme_item_list().
+ * Markup generated by item-list.html.twig.
  */
 .item-list .title {
   font-weight: bold;
@@ -418,7 +418,7 @@ ul.links a.active {
 }
 
 /**
- * Markup generated by theme_breadcrumb().
+ * Markup generated by breadcrumb.html.twig.
  */
 .breadcrumb {
   padding-bottom: 0.5em;
diff --git a/core/modules/system/lib/Drupal/system/SystemManager.php b/core/modules/system/lib/Drupal/system/SystemManager.php
index a17fde1..3f8304b 100644
--- a/core/modules/system/lib/Drupal/system/SystemManager.php
+++ b/core/modules/system/lib/Drupal/system/SystemManager.php
@@ -196,7 +196,7 @@ public function getBlockContents() {
    *   The menu item to be displayed.
    *
    * @return array
-   *   An array of menu items, as expected by theme_admin_block_content().
+   *   An array of menu items, as expected by admin-block-content.html.twig.
    */
   public function getAdminBlock($item) {
     if (!isset($item['mlid'])) {
diff --git a/core/modules/system/lib/Drupal/system/Tests/Theme/FunctionsTest.php b/core/modules/system/lib/Drupal/system/Tests/Theme/FunctionsTest.php
index 7aa294c..ea7fa86 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Theme/FunctionsTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Theme/FunctionsTest.php
@@ -33,7 +33,7 @@ public static function getInfo() {
   }
 
   /**
-   * Tests theme_item_list().
+   * Tests item-list.html.twig.
    */
   function testItemList() {
     // Verify that empty items produce no output.
diff --git a/core/modules/update/update.module b/core/modules/update/update.module
index db3b893..fc2d69e 100644
--- a/core/modules/update/update.module
+++ b/core/modules/update/update.module
@@ -561,7 +561,6 @@ function _update_project_status_sort($a, $b) {
  *   - last: The timestamp when the site last checked for available updates.
  *
  * @see theme_update_report()
- * @see theme_update_available_updates_form()
  * @ingroup themeable
  */
 function theme_update_last_check($variables) {
diff --git a/core/modules/views/lib/Drupal/views/Plugin/views/PluginBase.php b/core/modules/views/lib/Drupal/views/Plugin/views/PluginBase.php
index 086160d..cc57d75 100644
--- a/core/modules/views/lib/Drupal/views/Plugin/views/PluginBase.php
+++ b/core/modules/views/lib/Drupal/views/Plugin/views/PluginBase.php
@@ -26,9 +26,8 @@
  *   template engine extension).
  *   If a template file should be used, the file has to be placed in the
  *   module's templates folder.
- *   Example: theme = "mymodule_row" of module "mymodule" will implement either
- *   theme_mymodule_row() or mymodule-row.html.twig in the
- *   [..]/modules/mymodule/templates folder.
+ *   Example: theme = "mymodule_row" of module "mymodule" will implement
+ *   mymodule-row.html.twig in the [..]/modules/mymodule/templates folder.
  * - register_theme: (optional) When set to TRUE (default) the theme is
  *   registered automatically. When set to FALSE the plugin reuses an existing
  *   theme implementation, defined by another module or views plugin.