diff --git a/core/INSTALL.txt b/core/INSTALL.txt
index 18510eb989..2f763509bf 100644
--- a/core/INSTALL.txt
+++ b/core/INSTALL.txt
@@ -201,36 +201,40 @@ INSTALLATION
 
    b. Missing settings file.
 
-      Drupal will try to automatically create a settings.php configuration file,
-      which is normally in the directory sites/default (to avoid problems when
-      upgrading, Drupal is not packaged with this file). If auto-creation fails,
-      you will need to create this file yourself, using the file
-      sites/default/default.settings.php as a template.
+      Drupal will try to automatically create settings.php and services.yml
+      files, which are normally in the directory settings (to avoid
+      problems when upgrading, Drupal is not packaged with this file). If
+      auto-creation of either file fails, you will need to create the file
+      yourself. Use the template core/default.settings.php or
+      core/default.services.yml respectively.
 
       For example, on a Unix/Linux command line, you can make a copy of the
       default.settings.php file with the command:
 
-        cp sites/default/default.settings.php sites/default/settings.php
+        cp core/default.settings.php settings/settings.php
+        cp core/default.services.yml settings/services.yml
 
       Next, grant write privileges to the file to everyone (including the web
       server) with the command:
 
-        chmod a+w sites/default/settings.php
+        chmod a+w settings/settings.php
+        chmod a+w settings/services.yml
 
       Be sure to set the permissions back after the installation is finished!
       Sample command:
 
-        chmod go-w sites/default/settings.php
+        chmod go-w settings/settings.php
+        chmod go-w settings/services.yml
 
    c. Write permissions after install.
 
-      The install script will attempt to write-protect the settings.php file and
-      the sites/default directory after saving your configuration. If this
-      fails, you will be notified, and you can do it manually. Sample commands
-      from a Unix/Linux command line:
+      The install script will attempt to write-protect the settings.php file
+      after saving your configuration. If this fails, you will be notified, and
+      you can do it manually. Sample commands from a Unix/Linux command line:
 
-        chmod go-w sites/default/settings.php
-        chmod go-w sites/default
+        chmod go-w settings/settings.php
+        chmod go-w settings/services.yml
+        chmod go-w settings
 
 4. Verify that the site is working.
 
@@ -355,9 +359,9 @@ Drupal can be reinstalled without downloading and extracting the Drupal release.
 
 1. Drop all the tables in your database.
 
-2. Remove everything in sites/default/files.
+2. Remove everything in the files directory.
 
-3. Remove sites/default/settings.php.
+3. Remove settings.php.
 
 4. Follow the Installation Instructions above starting from Step 3 (Run the
    install script).
@@ -391,28 +395,28 @@ MULTISITE CONFIGURATION
 A single Drupal installation can host several Drupal-powered sites, each with
 its own individual configuration.
 
-For this to work you need the file sites/sites.php to exist. Make a copy of
-the example.sites.php file:
+For this to work you need to enable the commented out $sites variable in the
+settings.php in Drupal's root directory, like so:
 
-  $ cp sites/example.sites.php sites/sites.php
+  $sites = array();
 
 Additional site configurations are created in subdirectories within the 'sites'
 directory. Each subdirectory must have a 'settings.php' file, which specifies
 the configuration settings. The easiest way to create additional sites is to
-copy file 'default.settings.php' from the 'sites/default' directory into the
-new site directory with file name 'settings.php' and modify as appropriate.
+copy file 'core/default.settings.php' into the new site directory with file name
+'settings.php' and modify as appropriate.
+
 The new directory name is constructed from the site's URL. The configuration
 for www.example.com could be in 'sites/example.com/settings.php' (note that
 'www.' should be omitted if users can access your site at http://example.com/).
 
-  $ cp sites/default/defaults.settings.php sites/example.com/settings.php
+  $ cp core/default.settings.php sites/example.com/settings.php
 
 Sites do not have to have a different domain. You can also use subdomains and
 subdirectories for Drupal sites. For example, example.com, sub.example.com, and
 sub.example.com/site3 can all be defined as independent Drupal sites. The setup
 for a configuration such as this would look like the following:
 
-  sites/default/settings.php
   sites/example.com/settings.php
   sites/sub.example.com/settings.php
   sites/sub.example.com.site3/settings.php
@@ -427,7 +431,7 @@ first configuration it finds:
   sites/www.sub.example.com/settings.php
   sites/sub.example.com/settings.php
   sites/example.com/settings.php
-  sites/default/settings.php
+  settings.php
 
 If you are installing on a non-standard port, the port number is treated as the
 deepest subdomain. For example: http://www.example.com:8080/ could be loaded
diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index afd267adcf..56339ff2ec 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -161,6 +161,26 @@
  */
 define('DRUPAL_ROOT', dirname(dirname(__DIR__)));
 
+/**
+ * Returns the appropriate configuration directory.
+ *
+ * Temporary backwards-compatibility layer for Drush.
+ *
+ * @deprecated 8.x-dev
+ *   Use \Drupal\Core\Site\Site::getPath() instead.
+ *
+ * @internal
+ */
+function conf_path() {
+  if (strpos(debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS)[1]['function'], 'drush') === FALSE) {
+    throw new \Exception('conf_path() is retained for Drush compatibility only.');
+  }
+  // When called from _drush_bootstrap_drupal_site_validate() on testbots, this
+  // function is supposed to return the site path of the parent site, which is
+  // '' (the document root). Ensure that the returned path is relative.
+  // @see https://github.com/drush-ops/drush/blob/master/includes/bootstrap.inc#L782
+  return '.';
+}
 /**
  * Returns the path of a configuration directory.
  *
diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index 18f6a398bf..c4b0c2fb30 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -25,6 +25,7 @@
 use Drupal\Core\Language\LanguageManager;
 use Drupal\Core\Logger\LoggerChannelFactory;
 use Drupal\Core\Site\Settings;
+use Drupal\Core\Site\Site;
 use Drupal\Core\StringTranslation\Translator\FileTranslation;
 use Drupal\Core\StackMiddleware\ReverseProxyMiddleware;
 use Drupal\Core\StreamWrapper\PublicStream;
@@ -338,6 +339,12 @@ function install_begin_request($class_loader, &$install_state) {
   $site_path = empty($install_state['site_path']) ? DrupalKernel::findSitePath($request, FALSE) : $install_state['site_path'];
   Settings::initialize(dirname(dirname(__DIR__)), $site_path, $class_loader);
 
+  // Initialize the site directory.
+  // This primes the site path to be used during installation, to allow an empty
+  // site folder to be prepared in the /sites directory into which Drupal will
+  // be installed.
+  Site::initInstaller(DRUPAL_ROOT);
+
   // Ensure that procedural dependencies are loaded as early as possible,
   // since the error/exception handlers depend on them.
   require_once __DIR__ . '/../modules/system/system.install';
@@ -442,7 +449,7 @@ function install_begin_request($class_loader, &$install_state) {
     $directory = $GLOBALS['config']['locale.settings']['translation']['path'];
   }
   else {
-    $directory = $site_path . '/files/translations';
+    $directory = Site::getPath('files/translations');
   }
   $container->set('string_translator.file_translation', new FileTranslation($directory));
   $container->get('string_translation')
@@ -1174,8 +1181,7 @@ function install_verify_completed_task() {
 function install_verify_database_settings($site_path) {
   if ($database = Database::getConnectionInfo()) {
     $database = $database['default'];
-    $settings_file = './' . $site_path . '/settings.php';
-    $errors = install_database_errors($database, $settings_file);
+    $errors = install_database_errors($database);
     if (empty($errors)) {
       return TRUE;
     }
@@ -1909,9 +1915,8 @@ function install_check_translations($langcode, $server_pattern) {
   $readable = FALSE;
   $writable = FALSE;
   // @todo: Make this configurable.
-  $site_path = \Drupal::service('site.path');
-  $files_directory = $site_path . '/files';
-  $translations_directory = $site_path . '/files/translations';
+  $files_directory = Site::getPath('files');
+  $translations_directory = Site::getPath('files/translations');
   $translations_directory_exists = FALSE;
   $online = FALSE;
 
@@ -2088,8 +2093,9 @@ function install_check_requirements($install_state) {
     $readable = FALSE;
     $writable = FALSE;
     $site_path = './' . \Drupal::service('site.path');
-    $file = $site_path . "/{$default_file_info['file']}";
-    $default_file = "./sites/default/{$default_file_info['file_default']}";
+    $conf_path = './' . conf_path(FALSE);
+    $file = $conf_path . "/{$default_file_info['file']}";
+    $default_file = "./core/{$default_file_info['file_default']}";
     $exists = FALSE;
     // Verify that the directory exists.
     if (drupal_verify_install_file($site_path, FILE_EXIST, 'dir')) {
diff --git a/core/includes/install.inc b/core/includes/install.inc
index 45a8b141c3..c584daa7da 100644
--- a/core/includes/install.inc
+++ b/core/includes/install.inc
@@ -15,6 +15,7 @@
 use Drupal\Core\Extension\ExtensionDiscovery;
 use Drupal\Core\Extension\ModuleHandler;
 use Drupal\Core\Site\Settings;
+use Drupal\Core\Site\Site;
 
 /**
  * Requirement severity -- Informational message only.
@@ -219,7 +220,7 @@ function drupal_get_database_types() {
  */
 function drupal_rewrite_settings($settings = [], $settings_file = NULL) {
   if (!isset($settings_file)) {
-    $settings_file = \Drupal::service('site.path') . '/settings.php';
+    $settings_file = Site::getPath('settings.php');
   }
   // Build list of setting names and insert the values into the global namespace.
   $variable_names = [];
@@ -678,6 +679,9 @@ function drupal_install_system($install_state) {
  *
  * @return
  *   TRUE on success or FALSE on failure. A message is set for the latter.
+ *
+ * @todo Do not automatically call into drupal_install_fix_file().
+ * @see https://drupal.org/node/1616266
  */
 function drupal_verify_install_file($file, $mask = NULL, $type = 'file', $autofix = TRUE) {
   $return = TRUE;
diff --git a/core/includes/update.inc b/core/includes/update.inc
index 2021a66231..b6639ce481 100644
--- a/core/includes/update.inc
+++ b/core/includes/update.inc
@@ -66,6 +66,34 @@ function update_check_incompatibility($name, $type = 'module') {
   return FALSE;
 }
 
+/**
+ * Returns whether the settings file requirement has been satisfied.
+ *
+ * @return array
+ *  A requirements info array.
+ */
+function update_settings_file_requirements() {
+  $requirements = array();
+
+  // Check whether settings.php needs to be rewritten.
+  $settings_file = Site::getPath('settings.php');
+  $writable = drupal_verify_install_file($settings_file, FILE_EXIST | FILE_READABLE | FILE_WRITABLE);
+  $requirements['settings file']['title'] = 'Settings file';
+  if ($writable) {
+    $requirements['settings file'] += array(
+      'value' => 'settings.php is writable.',
+    );
+  }
+  else {
+    $requirements['settings file'] += array(
+      'value' => 'settings.php is not writable.',
+      'severity' => REQUIREMENT_ERROR,
+      'description' => 'Drupal requires write permissions to <em>' . $settings_file . '</em> during the update process. If you are unsure how to grant file permissions, consult the <a href="http://drupal.org/server-permissions">online handbook</a>.',
+    );
+  }
+  return $requirements;
+}
+
 /**
  * Returns whether the minimum schema requirement has been satisfied.
  *
diff --git a/core/lib/Drupal/Core/Database/Driver/sqlite/Install/Tasks.php b/core/lib/Drupal/Core/Database/Driver/sqlite/Install/Tasks.php
index f5cb289329..8f54a39e82 100644
--- a/core/lib/Drupal/Core/Database/Driver/sqlite/Install/Tasks.php
+++ b/core/lib/Drupal/Core/Database/Driver/sqlite/Install/Tasks.php
@@ -6,6 +6,7 @@
 use Drupal\Core\Database\Driver\sqlite\Connection;
 use Drupal\Core\Database\DatabaseNotFoundException;
 use Drupal\Core\Database\Install\Tasks as InstallTasks;
+use Drupal\Core\Site\Site;
 
 /**
  * Specifies installation tasks for SQLite databases.
diff --git a/core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php b/core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php
index 09d866f288..58875e62f9 100644
--- a/core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php
+++ b/core/lib/Drupal/Core/Installer/Form/SiteConfigureForm.php
@@ -6,6 +6,7 @@
 use Drupal\Core\Form\ConfigFormBase;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Locale\CountryManagerInterface;
+use Drupal\Core\Site\Site;
 use Drupal\Core\Site\Settings;
 use Drupal\Core\State\StateInterface;
 use Drupal\user\UserStorageInterface;
@@ -128,6 +129,7 @@ public function buildForm(array $form, FormStateInterface $form_state) {
     // Warn about settings.php permissions risk
     $settings_dir = $this->sitePath;
     $settings_file = $settings_dir . '/settings.php';
+
     // Check that $_POST is empty so we only show this message when the form is
     // first displayed, not on the next page after it is submitted. (We do not
     // want to repeat it multiple times because it is a general warning that is
diff --git a/core/lib/Drupal/Core/Installer/Form/SiteSettingsForm.php b/core/lib/Drupal/Core/Installer/Form/SiteSettingsForm.php
index b82bb01ae1..4d9d185e23 100644
--- a/core/lib/Drupal/Core/Installer/Form/SiteSettingsForm.php
+++ b/core/lib/Drupal/Core/Installer/Form/SiteSettingsForm.php
@@ -141,7 +141,6 @@ public function buildForm(array $form, FormStateInterface $form_state) {
     ];
 
     $form['errors'] = [];
-    $form['settings_file'] = ['#type' => 'value', '#value' => $settings_file];
 
     return $form;
   }
diff --git a/core/lib/Drupal/Core/Site/Settings.php b/core/lib/Drupal/Core/Site/Settings.php
index c6fbed659f..5f6f4f9dc4 100644
--- a/core/lib/Drupal/Core/Site/Settings.php
+++ b/core/lib/Drupal/Core/Site/Settings.php
@@ -121,8 +121,24 @@ public static function initialize($app_root, $site_path, &$class_loader) {
     $config = [];
     $databases = [];
 
-    if (is_readable($app_root . '/' . $site_path . '/settings.php')) {
-      require $app_root . '/' . $site_path . '/settings.php';
+    // Read the global /settings/settings.php file.
+    // Allow it to set/override the following variables:
+    $sites = NULL;
+    $conf_path = NULL;
+    // Exclude it for test requests to prevent settings of the test runner from
+    // leaking into the test environment.
+    if (!drupal_valid_test_ua() && is_readable(DRUPAL_ROOT . '/settings/settings.php')) {
+      require DRUPAL_ROOT . '/settings/settings.php';
+    }
+
+    // Discover the site directory.
+    Site::init(DRUPAL_ROOT, $sites, $conf_path);
+
+    // Read settings.php of the actual site, unless it is the root/default site.
+    // Concatenation is safe here, since $conf_path is known to be not empty.
+    $conf_path = Site::getPath();
+    if ($conf_path !== '' && is_readable(DRUPAL_ROOT . '/' . $conf_path . '/settings.php')) {
+      require DRUPAL_ROOT . '/' . $conf_path . '/settings.php';
     }
 
     // Initialize Database.
diff --git a/core/modules/content_moderation/src/Form/ContentModerationConfigureForm.php b/core/modules/content_moderation/src/Form/ContentModerationConfigureForm.php
index f43451ec63..7e87604983 100644
--- a/core/modules/content_moderation/src/Form/ContentModerationConfigureForm.php
+++ b/core/modules/content_moderation/src/Form/ContentModerationConfigureForm.php
@@ -113,6 +113,7 @@ public function buildConfigurationForm(array $form, FormStateInterface $form_sta
         ],
         'operations' => [
           '#type' => 'operations',
+          '#attached' => ['library' => ['core/drupal.dialog.ajax']],
           '#links' => [
             'select' => [
               'title' => $this->t('Select'),
diff --git a/core/modules/content_moderation/tests/src/Functional/ContentModerationWorkflowTypeTest.php b/core/modules/content_moderation/tests/src/Functional/ContentModerationWorkflowTypeTest.php
index cbe5807a5f..5fd9e2b59f 100644
--- a/core/modules/content_moderation/tests/src/Functional/ContentModerationWorkflowTypeTest.php
+++ b/core/modules/content_moderation/tests/src/Functional/ContentModerationWorkflowTypeTest.php
@@ -92,7 +92,9 @@ public function testNewWorkflow() {
     $session->fieldDisabled('type_settings[published]');
     $session->fieldDisabled('type_settings[default_revision]');
 
-    $this->drupalGet('admin/config/workflow/workflows/manage/test/type/node');
+    $this->drupalGet('admin/config/workflow/workflows/manage/test');
+    $this->assertSession()->libraryAttached('core/drupal.dialog.ajax');
+    $this->clickLink('Select');
     $session->pageTextContains('Select the content types for the Test workflow');
     foreach ($types as $type) {
       $session->pageTextContains($type->label());
diff --git a/core/modules/file/tests/file_test/src/StreamWrapper/DummyReadOnlyStreamWrapper.php b/core/modules/file/tests/file_test/src/StreamWrapper/DummyReadOnlyStreamWrapper.php
index c1c36af413..91f0e80cf4 100644
--- a/core/modules/file/tests/file_test/src/StreamWrapper/DummyReadOnlyStreamWrapper.php
+++ b/core/modules/file/tests/file_test/src/StreamWrapper/DummyReadOnlyStreamWrapper.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\file_test\StreamWrapper;
 
+use Drupal\Core\Site\Site;
 use Drupal\Core\StreamWrapper\LocalReadOnlyStream;
 
 /**
diff --git a/core/modules/file/tests/file_test/src/StreamWrapper/DummyStreamWrapper.php b/core/modules/file/tests/file_test/src/StreamWrapper/DummyStreamWrapper.php
index 6ce842470f..4ec2612107 100644
--- a/core/modules/file/tests/file_test/src/StreamWrapper/DummyStreamWrapper.php
+++ b/core/modules/file/tests/file_test/src/StreamWrapper/DummyStreamWrapper.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\file_test\StreamWrapper;
 
+use Drupal\Core\Site\Site;
 use Drupal\Core\StreamWrapper\LocalStream;
 
 /**
diff --git a/core/modules/simpletest/src/TestBase.php b/core/modules/simpletest/src/TestBase.php
index b47d2d7e85..e9fc31a211 100644
--- a/core/modules/simpletest/src/TestBase.php
+++ b/core/modules/simpletest/src/TestBase.php
@@ -9,6 +9,7 @@
 use Drupal\Core\Database\Database;
 use Drupal\Core\File\FileSystemInterface;
 use Drupal\Core\Site\Settings;
+use Drupal\Core\Site\Site;
 use Drupal\Core\StreamWrapper\PublicStream;
 use Drupal\Core\Test\TestDatabase;
 use Drupal\Core\Test\TestSetupTrait;
@@ -1169,7 +1170,11 @@ private function prepareEnvironment() {
 
     // After preparing the environment and changing the database prefix, we are
     // in a valid test environment.
+    if (!is_dir(DRUPAL_ROOT . '/' . $this->siteDirectory)) {
+      throw new \RuntimeException("Test site directory '$this->siteDirectory' does not exist.");
+    }
     drupal_valid_test_ua($this->databasePrefix);
+    Site::setUpTest();
 
     // Reset settings.
     new Settings([
@@ -1283,6 +1288,11 @@ private function restoreEnvironment() {
       drupal_valid_test_ua(FALSE);
     }
 
+    Site::tearDownTest();
+
+    // Restore stream wrappers of the test runner.
+    file_get_stream_wrappers();
+
     // Restore original shutdown callbacks.
     $callbacks = &drupal_register_shutdown_function();
     $callbacks = $this->originalShutdownCallbacks;
diff --git a/core/tests/Drupal/KernelTests/Core/DrupalKernel/DrupalKernelTest.php b/core/tests/Drupal/KernelTests/Core/DrupalKernel/DrupalKernelTest.php
index b5cb96b8cc..4f287586e8 100644
--- a/core/tests/Drupal/KernelTests/Core/DrupalKernel/DrupalKernelTest.php
+++ b/core/tests/Drupal/KernelTests/Core/DrupalKernel/DrupalKernelTest.php
@@ -4,6 +4,7 @@
 
 use Drupal\Core\DrupalKernel;
 use Drupal\KernelTests\KernelTestBase;
+use Drupal\Core\Site\Site;
 use Symfony\Component\HttpFoundation\Request;
 
 /**
@@ -17,6 +18,9 @@ class DrupalKernelTest extends KernelTestBase {
    * {@inheritdoc}
    */
   protected function setUp() {
+    // Initialize the test Site singleton, so that Site::getPath() works.
+    Site::init(DRUPAL_ROOT);
+
     // DrupalKernel relies on global $config_directories and requires those
     // directories to exist. Therefore, create the directories, but do not
     // invoke KernelTestBase::setUp(), since that would set up further
diff --git a/core/tests/Drupal/KernelTests/Core/File/ReadOnlyStreamWrapperTest.php b/core/tests/Drupal/KernelTests/Core/File/ReadOnlyStreamWrapperTest.php
index 00dfa0b8d3..413aa6bd5f 100644
--- a/core/tests/Drupal/KernelTests/Core/File/ReadOnlyStreamWrapperTest.php
+++ b/core/tests/Drupal/KernelTests/Core/File/ReadOnlyStreamWrapperTest.php
@@ -2,6 +2,7 @@
 
 namespace Drupal\KernelTests\Core\File;
 
+use Drupal\Core\Site\Site;
 use Drupal\Core\StreamWrapper\StreamWrapperInterface;
 use Drupal\file_test\StreamWrapper\DummyReadOnlyStreamWrapper;
 
diff --git a/core/tests/Drupal/KernelTests/Core/Site/SettingsRewriteTest.php b/core/tests/Drupal/KernelTests/Core/Site/SettingsRewriteTest.php
index 0507871124..623616ab31 100644
--- a/core/tests/Drupal/KernelTests/Core/Site/SettingsRewriteTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Site/SettingsRewriteTest.php
@@ -4,6 +4,7 @@
 
 use Drupal\Core\Site\Settings;
 use Drupal\KernelTests\KernelTestBase;
+use Drupal\Core\Site\Site;
 
 /**
  * Tests the drupal_rewrite_settings() function.
diff --git a/core/tests/Drupal/Tests/WebAssert.php b/core/tests/Drupal/Tests/WebAssert.php
index 4f7a7d292c..c06edba58c 100644
--- a/core/tests/Drupal/Tests/WebAssert.php
+++ b/core/tests/Drupal/Tests/WebAssert.php
@@ -597,4 +597,37 @@ public function pageTextContainsOnce($text) {
     throw new ResponseTextException($message, $this->session->getDriver());
   }
 
+  /**
+   * Get the Drupal settings for the current page.
+   *
+   * @return array
+   *   An array of Drupal settings for the current page.
+   */
+  protected function getDrupalSettings() {
+    return json_decode($this->session->getPage()->find('css', '[data-drupal-selector="drupal-settings-json"]')->getHtml(), TRUE);
+  }
+
+  /**
+   * Assert a library has been attached to the current page.
+   *
+   * @param string $library_name
+   *   The name of the library which should appear on the current page.
+   *
+   * @throws \Behat\Mink\Exception\ExpectationException
+   */
+  public function libraryAttached($library_name) {
+    $drupal_settings = $this->getDrupalSettings();
+    $libraries = isset($drupal_settings['ajaxPageState']['libraries']) ? explode(',', $drupal_settings['ajaxPageState']['libraries']) : [];
+    $this->assert(in_array($library_name, $libraries), sprintf('The library "%s" should exist on the current page, but it does not.', $library_name));
+  }
+
+  /**
+   * Assert a library has been attached to the current page.
+   */
+  public function libraryNotAttached($library_name) {
+    $drupal_settings = $this->getDrupalSettings();
+    $libraries = isset($drupal_settings['ajaxPageState']['libraries']) ? explode(',', $drupal_settings['ajaxPageState']['libraries']) : [];
+    $this->assert(!in_array($library_name, $libraries), sprintf('The library "%s" should not exist on the current page, but it does.', $library_name));
+  }
+
 }
diff --git a/sites/default/default.settings.php b/sites/default/default.settings.php
index ae64d2ffe8..5bcecc267f 100644
--- a/sites/default/default.settings.php
+++ b/sites/default/default.settings.php
@@ -342,10 +342,11 @@
  * configuration requires the IP addresses of all remote proxies to be
  * specified in $settings['reverse_proxy_addresses'] to work correctly.
  *
- * Enable this setting to get Drupal to determine the client IP from the
- * X-Forwarded-For header. If you are unsure about this setting, do not have a
- * reverse proxy, or Drupal operates in a shared hosting environment, this
- * setting should remain commented out.
+ * Enable this setting to get Drupal to determine the client IP from
+ * the X-Forwarded-For header (or $settings['reverse_proxy_header'] if set).
+ * If you are unsure about this setting, do not have a reverse proxy,
+ * or Drupal operates in a shared hosting environment, this setting
+ * should remain commented out.
  *
  * In order for this setting to be used you must specify every possible
  * reverse proxy IP address in $settings['reverse_proxy_addresses'].
@@ -364,35 +365,34 @@
 # $settings['reverse_proxy_addresses'] = ['a.b.c.d', ...];
 
 /**
- * Reverse proxy trusted headers.
- *
- * Sets which headers to trust from your reverse proxy.
- *
- * Common values are:
- * - \Symfony\Component\HttpFoundation\Request::HEADER_X_FORWARDED_ALL
- * - \Symfony\Component\HttpFoundation\Request::HEADER_FORWARDED
- *
- * Note the default value of
- * @code
- * \Symfony\Component\HttpFoundation\Request::HEADER_X_FORWARDED_ALL | \Symfony\Component\HttpFoundation\Request::HEADER_FORWARDED
- * @endcode
- * is not secure by default. The value should be set to only the specific
- * headers the reverse proxy uses. For example:
- * @code
- * \Symfony\Component\HttpFoundation\Request::HEADER_X_FORWARDED_ALL
- * @endcode
- * This would trust the following headers:
- * - X_FORWARDED_FOR
- * - X_FORWARDED_HOST
- * - X_FORWARDED_PROTO
- * - X_FORWARDED_PORT
- *
- * @see \Symfony\Component\HttpFoundation\Request::HEADER_X_FORWARDED_ALL
- * @see \Symfony\Component\HttpFoundation\Request::HEADER_FORWARDED
- * @see \Symfony\Component\HttpFoundation\Request::setTrustedProxies
+ * Set this value if your proxy server sends the client IP in a header
+ * other than X-Forwarded-For.
  */
-# $settings['reverse_proxy_trusted_headers'] = \Symfony\Component\HttpFoundation\Request::HEADER_X_FORWARDED_ALL | \Symfony\Component\HttpFoundation\Request::HEADER_FORWARDED;
+# $settings['reverse_proxy_header'] = 'X_CLUSTER_CLIENT_IP';
 
+/**
+ * Set this value if your proxy server sends the client protocol in a header
+ * other than X-Forwarded-Proto.
+ */
+# $settings['reverse_proxy_proto_header'] = 'X_FORWARDED_PROTO';
+
+/**
+ * Set this value if your proxy server sends the client protocol in a header
+ * other than X-Forwarded-Host.
+ */
+# $settings['reverse_proxy_host_header'] = 'X_FORWARDED_HOST';
+
+/**
+ * Set this value if your proxy server sends the client protocol in a header
+ * other than X-Forwarded-Port.
+ */
+# $settings['reverse_proxy_port_header'] = 'X_FORWARDED_PORT';
+
+/**
+ * Set this value if your proxy server sends the client protocol in a header
+ * other than Forwarded.
+ */
+# $settings['reverse_proxy_forwarded_header'] = 'FORWARDED';
 
 /**
  * Page caching: