diff --git a/core/lib/Drupal/Core/Update/UpdateKernel.php b/core/lib/Drupal/Core/Update/UpdateKernel.php
index 4005af7..80f243c 100755
--- a/core/lib/Drupal/Core/Update/UpdateKernel.php
+++ b/core/lib/Drupal/Core/Update/UpdateKernel.php
@@ -39,7 +39,8 @@ public function discoverServiceProviders() {
    * {@inheritdoc}
    */
   protected function initializeContainer() {
-    // Always force a container rebuild.
+    // Always force a container rebuild, in order to be able to override some
+    // services, see \Drupal\Core\Update\UpdateServiceProvider.
     $this->containerNeedsRebuild = TRUE;
     $container = parent::initializeContainer();
     return $container;
@@ -49,7 +50,8 @@ protected function initializeContainer() {
    * {@inheritdoc}
    */
   protected function cacheDrupalContainer(array $container_definition) {
-    // Don't save this particular container to cache.
+    // Don't save this particular container to cache, so it does not leak into
+    // the main site at all.
     return FALSE;
   }
 
diff --git a/core/modules/system/src/Controller/DbUpdateController.php b/core/modules/system/src/Controller/DbUpdateController.php
index 935a067..fa8104d 100644
--- a/core/modules/system/src/Controller/DbUpdateController.php
+++ b/core/modules/system/src/Controller/DbUpdateController.php
@@ -186,9 +186,6 @@ public function handle($op, Request $request) {
     }
     $title = isset($output['#title']) ? $output['#title'] : $this->t('Drupal database update');
 
-    // Ensure that at least the drupalSettings js is loaded.
-    $output['#attached']['library'][] = 'core/drupalSettings';
-
     return $this->bareHtmlPageRenderer->renderBarePage($output, $title, 'maintenance_page', $regions);
   }
 
diff --git a/core/modules/system/src/Tests/Update/UpdatePathTestBase.php b/core/modules/system/src/Tests/Update/UpdatePathTestBase.php
index e666afe..cd6d790 100644
--- a/core/modules/system/src/Tests/Update/UpdatePathTestBase.php
+++ b/core/modules/system/src/Tests/Update/UpdatePathTestBase.php
@@ -236,9 +236,9 @@ protected function runUpdates() {
     ]]]);
 
     $this->drupalGet($this->updateUrl);
-    $this->doPreUpdateTests();
     $this->clickLink(t('Continue'));
 
+    $this->doSelectionTest();
     // Run the update hooks.
     $this->clickLink(t('Apply pending updates'));
 
@@ -275,11 +275,12 @@ protected function replaceUser1() {
   }
 
   /**
-   * Tests update.php before tests are run.
+   * Tests the selection page.
    */
-  protected function doPreUpdateTests() {
-    // No-op. Tests wishing to do tests at the update.php URL before updates are
-    // run can override this method and implement their required tests.
+  protected function doSelectionTest() {
+    // No-op. Tests wishing to do test the selection page or the general
+    //update.php environment before running update.php can override this
+    //method and implement their required tests.
   }
 
 }
diff --git a/core/modules/system/src/Tests/Update/UpdatePathTestJavaScriptTest.php b/core/modules/system/src/Tests/Update/UpdatePathTestJavaScriptTest.php
index 0061890..cc6ba4c 100644
--- a/core/modules/system/src/Tests/Update/UpdatePathTestJavaScriptTest.php
+++ b/core/modules/system/src/Tests/Update/UpdatePathTestJavaScriptTest.php
@@ -35,7 +35,7 @@ public function testJavaScriptLoading() {
   /**
    * {@inheritdoc}
    */
-  protected function doPreUpdateTests() {
+  protected function doSelectionTest() {
     // Ensure that at least one JS script has drupalSettings in there.
     $scripts = $this->xpath('//script');
     $found = FALSE;