diff --git a/core/lib/Drupal/Component/Utility/SafeMarkup.php b/core/lib/Drupal/Component/Utility/SafeMarkup.php
index e7f3c63..4f11c49 100644
--- a/core/lib/Drupal/Component/Utility/SafeMarkup.php
+++ b/core/lib/Drupal/Component/Utility/SafeMarkup.php
@@ -133,7 +133,7 @@ public static function setMultiple(array $safe_strings) {
       foreach ($strategies as $strategy => $value) {
         $string = (string) $string;
         if (is_numeric($value)) {
-          static::set($string, $strategy);
+          static::$safeStrings[$string][$strategy] = $value;
         }
         else {
           // Danger - something is very wrong.
@@ -154,7 +154,13 @@ public static function setMultiple(array $safe_strings) {
    *   self::set(), it won't be escaped again.
    */
   public static function escape($string) {
-    return static::isSafe($string) ? $string : static::checkPlain($string);
+    if (static::isSafe($string)) {
+      static::set($string);
+      return $string;
+    }
+    else {
+      return static::checkPlain($string);
+    }
   }
 
   /**
@@ -170,7 +176,13 @@ public static function escape($string) {
    * @see \Drupal\Component\Utility\Xss::filterAdmin()
    */
   public static function checkAdminXss($string) {
-    return static::isSafe($string) ? $string : Xss::filterAdmin($string);
+    if (static::isSafe($string)) {
+      static::set($string);
+      return $string;
+    }
+    else {
+      return static::set(Xss::filterAdmin($string));
+    }
   }
 
   /**
diff --git a/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php b/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php
index e5cdd87..5e5bf00 100644
--- a/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php
+++ b/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php
@@ -9,6 +9,7 @@
 
 use Drupal\Component\Plugin\PluginManagerInterface;
 use Drupal\Component\Utility\NestedArray;
+use Drupal\Component\Utility\SafeMarkup;
 use Drupal\Core\Cache\CacheableMetadata;
 use Drupal\Core\Cache\CacheableResponse;
 use Drupal\Core\Cache\CacheContextsManager;
@@ -263,7 +264,7 @@ protected function prepare(array $main_content, Request $request, RouteMatchInte
 
     // Determine the title: use the title provided by the main content if any,
     // otherwise get it from the routing information.
-    $title = isset($main_content['#title']) ? $main_content['#title'] : $this->titleResolver->getTitle($request, $route_match->getRouteObject());
+    $title = isset($main_content['#title']) ? SafeMarkup::set($main_content['#title']) : $this->titleResolver->getTitle($request, $route_match->getRouteObject());
 
     return [$page, $title];
   }
diff --git a/core/modules/filter/src/Tests/FilterAdminTest.php b/core/modules/filter/src/Tests/FilterAdminTest.php
index 1dccd5d..02045bc 100644
--- a/core/modules/filter/src/Tests/FilterAdminTest.php
+++ b/core/modules/filter/src/Tests/FilterAdminTest.php
@@ -372,8 +372,8 @@ function testFilterTipHtmlEscape() {
     // Therefore we test only some parts.
     $link = '<a href="' . $base_url . '">' . SafeMarkup::checkPlain(\Drupal::config('system.site')->get('name')) . '</a>';
     $ampersand = '&amp;';
-    $link_as_code = '<code>' . $link . '</code>';
-    $ampersand_as_code = '<code>' . $ampersand . '</code>';
+    $link_as_code = '<code>' . SafeMarkup::checkPlain($link) . '</code>';
+    $ampersand_as_code = '<code>' . SafeMarkup::checkPlain($ampersand) . '</code>';
 
     $this->drupalGet('filter/tips');
 
diff --git a/core/modules/system/src/Tests/Theme/FunctionsTest.php b/core/modules/system/src/Tests/Theme/FunctionsTest.php
index a9a3dae..25721bb 100644
--- a/core/modules/system/src/Tests/Theme/FunctionsTest.php
+++ b/core/modules/system/src/Tests/Theme/FunctionsTest.php
@@ -167,24 +167,7 @@ function testItemList() {
     $this->assertThemeOutput('item_list', $variables, $expected);
   }
 
-  /**
-   * Tests links.html.twig.
-   */
-  function testLinks() {
-    // Turn off the query for the _l() function to compare the active
-    // link correctly.
-    $original_query = \Drupal::request()->query->all();
-    \Drupal::request()->query->replace(array());
-    // Verify that empty variables produce no output.
-    $variables = array();
-    $expected = '';
-    $this->assertThemeOutput('links', $variables, $expected, 'Empty %callback generates no output.');
-
-    $variables = array();
-    $variables['heading'] = 'Some title';
-    $expected = '';
-    $this->assertThemeOutput('links', $variables, $expected, 'Empty %callback with heading generates no output.');
-
+  protected function getVariables() {
     // Verify that a list of links is properly rendered.
     $variables = array();
     $variables['attributes'] = array('id' => 'somelinks');
@@ -215,6 +198,26 @@ function testLinks() {
         )
       ),
     );
+    return $variables;
+  }
+
+  /**
+   * Tests links.html.twig.
+   */
+  function testLinks() {
+    // Turn off the query for the _l() function to compare the active
+    // link correctly.
+    $original_query = \Drupal::request()->query->all();
+    \Drupal::request()->query->replace(array());
+    // Verify that empty variables produce no output.
+    $variables = array();
+    $expected = '';
+    $this->assertThemeOutput('links', $variables, $expected, 'Empty %callback generates no output.');
+
+    $variables = array();
+    $variables['heading'] = 'Some title';
+    $expected = '';
+    $this->assertThemeOutput('links', $variables, $expected, 'Empty %callback with heading generates no output.');
 
     $expected_links = '';
     $expected_links .= '<ul id="somelinks">';
@@ -228,6 +231,7 @@ function testLinks() {
     $expected_links .= '</ul>';
 
     // Verify that passing a string as heading works.
+    $variables = $this->getVariables();
     $variables['heading'] = 'Links heading';
     $expected_heading = '<h2>Links heading</h2>';
     $expected = $expected_heading . $expected_links;
@@ -237,6 +241,8 @@ function testLinks() {
     \Drupal::request()->query->replace($original_query);
 
     // Verify that passing an array as heading works (core support).
+
+    $variables = $this->getVariables();
     $variables['heading'] = array(
       'text' => 'Links heading',
       'level' => 'h3',
@@ -247,12 +253,15 @@ function testLinks() {
     $this->assertThemeOutput('links', $variables, $expected);
 
     // Verify that passing attributes for the heading works.
+    $variables = $this->getVariables();
     $variables['heading'] = array('text' => 'Links heading', 'level' => 'h3', 'attributes' => array('id' => 'heading'));
     $expected_heading = '<h3 id="heading">Links heading</h3>';
     $expected = $expected_heading . $expected_links;
     $this->assertThemeOutput('links', $variables, $expected);
 
     // Verify that passing attributes for the links work.
+    $variables = $this->getVariables();
+    $variables['heading'] = array('text' => 'Links heading', 'level' => 'h3', 'attributes' => array('id' => 'heading'));
     $variables['links']['plain text']['attributes'] = array(
       'class' => array('a/class'),
     );
@@ -271,7 +280,12 @@ function testLinks() {
 
     // Verify the data- attributes for setting the "active" class on links.
     \Drupal::currentUser()->setAccount(new UserSession(array('uid' => 1)));
+    $variables = $this->getVariables();
+    $variables['heading'] = array('text' => 'Links heading', 'level' => 'h3', 'attributes' => array('id' => 'heading'));
     $variables['set_active_class'] = TRUE;
+    $variables['links']['plain text']['attributes'] = array(
+      'class' => array('a/class'),
+    );
     $expected_links = '';
     $expected_links .= '<ul id="somelinks">';
     $expected_links .= '<li class="a-link"><a href="' . Url::fromUri('base:a/link')->toString() . '">' . SafeMarkup::checkPlain('A <link>') . '</a></li>';
diff --git a/core/tests/Drupal/Tests/Core/Form/FormCacheTest.php b/core/tests/Drupal/Tests/Core/Form/FormCacheTest.php
index 1d9a67a..c5a43ea 100644
--- a/core/tests/Drupal/Tests/Core/Form/FormCacheTest.php
+++ b/core/tests/Drupal/Tests/Core/Form/FormCacheTest.php
@@ -347,7 +347,7 @@ public function testLoadCachedFormStateWithSafeStrings() {
       ->willReturn(TRUE);
 
     $cached_form_state = ['build_info' => ['safe_strings' => [
-      'a_safe_string' => ['html' => TRUE],
+      'a_safe_string' => ['html' => 1],
     ]]];
     $this->formStateCacheStore->expects($this->once())
       ->method('get')
@@ -448,7 +448,7 @@ public function testSetCacheWithSafeStrings() {
 
     $form_state_data = $form_state->getCacheableArray();
     $form_state_data['build_info']['safe_strings'] = [
-      'a_safe_string' => ['html' => TRUE],
+      'a_safe_string' => ['html' => 1],
     ];
     $this->formStateCacheStore->expects($this->once())
       ->method('setWithExpire')