diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index b6cce93..9c91043 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -787,7 +787,7 @@ function watchdog_exception($type, Exception $exception, $message = NULL, $varia
  *   If there are no messages set, the function returns NULL.
  *
  * @see drupal_get_messages()
- * @see theme_status_messages()
+ * @see status-messages.html.twig
  */
 function drupal_set_message($message = NULL, $type = 'status', $repeat = FALSE) {
   if (isset($message)) {
@@ -833,7 +833,7 @@ function drupal_set_message($message = NULL, $type = 'status', $repeat = FALSE) 
  *   drupal_set_message() for the array structure of individual messages.
  *
  * @see drupal_set_message()
- * @see theme_status_messages()
+ * @see status-messages.html.twig
  */
 function drupal_get_messages($type = NULL, $clear_queue = TRUE) {
   if ($messages = drupal_set_message()) {
diff --git a/core/includes/form.inc b/core/includes/form.inc
index d5eaa54..1ab8c3b 100644
--- a/core/includes/form.inc
+++ b/core/includes/form.inc
@@ -572,7 +572,7 @@ function template_preprocess_form_element(&$variables) {
  *
  * Form element labels include the #title and a #required marker. The label is
  * associated with the element itself by the element #id. Labels may appear
- * before or after elements, depending on theme_form_element() and
+ * before or after elements, depending on form-element.html.twig and
  * #title_display.
  *
  * This function will not be called for elements with no labels, depending on
diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index 303db67..2aafaa3 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -1420,9 +1420,9 @@ function template_preprocess_item_list(&$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
@@ -1890,7 +1890,7 @@ 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 79688ec..c5f60b3 100644
--- a/core/lib/Drupal/Component/Utility/SortArray.php
+++ b/core/lib/Drupal/Component/Utility/SortArray.php
@@ -77,7 +77,6 @@ class SortArray {
    *
    * 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 dd2bcd8..720841c 100644
--- a/core/lib/Drupal/Core/Form/FormBuilder.php
+++ b/core/lib/Drupal/Core/Form/FormBuilder.php
@@ -614,9 +614,9 @@ class FormBuilder implements FormBuilderInterface, FormValidatorInterface, FormS
 
     $build_info = $form_state->getBuildInfo();
     // If no #theme has been set, automatically apply theme suggestions.
-    // theme_form() itself is in #theme_wrappers and not #theme. Therefore, the
-    // #theme function only has to care for rendering the inner form elements,
-    // not the form itself.
+    // form.html.twig itself is in #theme_wrappers and not #theme. Therefore,
+    // the #theme function only has to care for rendering the inner form
+    // elements, not the form itself.
     if (!isset($form['#theme'])) {
       $form['#theme'] = array($form_id);
       if (isset($build_info['base_form_id'])) {
diff --git a/core/modules/block/templates/block-list.html.twig b/core/modules/block/templates/block-list.html.twig
index 474c654..854d3ce 100644
--- a/core/modules/block/templates/block-list.html.twig
+++ b/core/modules/block/templates/block-list.html.twig
@@ -5,7 +5,7 @@
  *
  * This template will be used when a block edit form specifies 'block_edit_form'
  * as its #theme callback.  Otherwise, by default, block add/edit forms will be
- * themed by theme_form().
+ * themed by form.html.twig.
  *
  * Available variables:
  * - form: The block add/edit form.
diff --git a/core/modules/book/book.module b/core/modules/book/book.module
index cea9627..d77b578 100644
--- a/core/modules/book/book.module
+++ b/core/modules/book/book.module
@@ -501,7 +501,7 @@ function template_preprocess_book_node_export_html(&$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'] = $variables['tree']['#children'];
diff --git a/core/modules/node/templates/node-edit-form.html.twig b/core/modules/node/templates/node-edit-form.html.twig
index e34baf9..6d8ac2a 100644
--- a/core/modules/node/templates/node-edit-form.html.twig
+++ b/core/modules/node/templates/node-edit-form.html.twig
@@ -7,7 +7,7 @@
  *
  * This template will be used when a node edit form specifies 'node_edit_form'
  * as its #theme callback.  Otherwise, by default, node add/edit forms will be
- * themed by theme_form().
+ * themed by form.html.twig.
  *
  * Available variables:
  * - form: The node add/edit form.
diff --git a/core/modules/rdf/rdf.module b/core/modules/rdf/rdf.module
index 371be2c..4cd6a3e 100644
--- a/core/modules/rdf/rdf.module
+++ b/core/modules/rdf/rdf.module
@@ -538,7 +538,7 @@ function rdf_preprocess_taxonomy_term(&$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 2cc44e7..991ad72 100644
--- a/core/modules/system/css/system.theme.css
+++ b/core/modules/system/css/system.theme.css
@@ -11,7 +11,7 @@
 }
 
 /**
- * Markup generated by theme_tablesort_indicator().
+ * Markup generated by tablesort-indicator.html.twig.
  */
 th.active img {
   display: inline;
@@ -21,7 +21,7 @@ td.active {
 }
 
 /**
- * Markup generated by theme_item_list().
+ * Markup generated by item-list.html.twig.
  */
 .item-list .title {
   font-weight: bold;
@@ -398,7 +398,7 @@ 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/src/SystemManager.php b/core/modules/system/src/SystemManager.php
index 145705f..0107453 100644
--- a/core/modules/system/src/SystemManager.php
+++ b/core/modules/system/src/SystemManager.php
@@ -195,7 +195,7 @@ class SystemManager {
    *   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(MenuLinkInterface $instance) {
     $content = array();
diff --git a/core/modules/system/src/Tests/Theme/FunctionsTest.php b/core/modules/system/src/Tests/Theme/FunctionsTest.php
index f9a4a83..c1ad1c7 100644
--- a/core/modules/system/src/Tests/Theme/FunctionsTest.php
+++ b/core/modules/system/src/Tests/Theme/FunctionsTest.php
@@ -28,7 +28,7 @@ class FunctionsTest extends WebTestBase {
   public static $modules = array('router_test');
 
   /**
-   * Tests theme_item_list().
+   * Tests item-list.html.twig.
    */
   function testItemList() {
     // Verify that empty items produce no output.
diff --git a/core/modules/views/src/Plugin/views/PluginBase.php b/core/modules/views/src/Plugin/views/PluginBase.php
index ccb86e3..dc48f28 100644
--- a/core/modules/views/src/Plugin/views/PluginBase.php
+++ b/core/modules/views/src/Plugin/views/PluginBase.php
@@ -28,9 +28,8 @@
  *   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.