core/modules/file/src/Tests/DownloadTest.php       |  1 -
 .../image/src/Tests/ImageStylesPathAndUrlTest.php  |  1 -
 core/modules/page_cache/page_cache.module          | 39 +++++++++++++++++++---
 .../src/Tests/PageCacheTagsIntegrationTest.php     |  5 +++
 core/modules/system/src/Form/PerformanceForm.php   |  3 +-
 .../system/src/Tests/Session/SessionTest.php       |  1 -
 core/modules/system/system.module                  |  2 +-
 7 files changed, 43 insertions(+), 9 deletions(-)

diff --git a/core/modules/file/src/Tests/DownloadTest.php b/core/modules/file/src/Tests/DownloadTest.php
index 165a76a..130b07c 100644
--- a/core/modules/file/src/Tests/DownloadTest.php
+++ b/core/modules/file/src/Tests/DownloadTest.php
@@ -57,7 +57,6 @@ public function testPrivateFileTransferWithoutPageCache() {
   public function testPrivateFileTransferWithPageCache() {
     // Turn on page caching and rerun the test.
     $this->assertTrue($this->container->get('module_installer')->install(['page_cache']), 'Page cache module installed.');
-    $this->rebuildContainer();
     $config = $this->config('system.performance');
     $config->set('cache.page.max_age', 300);
     $config->save();
diff --git a/core/modules/image/src/Tests/ImageStylesPathAndUrlTest.php b/core/modules/image/src/Tests/ImageStylesPathAndUrlTest.php
index dba4cec..ebaa81c 100644
--- a/core/modules/image/src/Tests/ImageStylesPathAndUrlTest.php
+++ b/core/modules/image/src/Tests/ImageStylesPathAndUrlTest.php
@@ -248,7 +248,6 @@ function doImageStyleUrlAndPathTests($scheme, $clean_url = TRUE, $extra_slash =
   protected function enablePageCache() {
     // Turn on page caching and rerun the test.
     $this->assertTrue($this->container->get('module_installer')->install(['page_cache']), 'Page cache module installed.');
-    $this->rebuildContainer();
     $config = $this->config('system.performance');
     $config->set('cache.page.max_age', 300);
     $config->save();
diff --git a/core/modules/page_cache/page_cache.module b/core/modules/page_cache/page_cache.module
index 9f01823..2c7d01f 100644
--- a/core/modules/page_cache/page_cache.module
+++ b/core/modules/page_cache/page_cache.module
@@ -1,18 +1,49 @@
 <?php
 
-// @todo
-//function page_cache_help() {}
+/**
+ * @file
+ * Caches responses for anonymous users, request and response policies allowing.
+ */
+
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\PageCache\RequestPolicyInterface;
+use Drupal\Core\Routing\RouteMatchInterface;
+
+/**
+ * Implements hook_help().
+ */
+function page_cache_help($route_name, RouteMatchInterface $route_match) {
+  switch ($route_name) {
+    case 'help.page.page_cache':
+      $output = '<h3>' . t('About') . '</h3>';
+      $output .= '<p>' . t('The Internal page cache module caches pages for anonymous users in the database.') . '</p>';
+      $output .= '<h3>' . t('Uses') . '</h3>';
+      $output .= '<dl>';
+      $output .= '<dt>' . t('Speeding up your site') . '</dt>';
+      $output .= '<dd>';
+      $output .= '<p>' . t('Pages requested by anonymous users are stored in a compressed format; depending on your site configuration and the amount of your web traffic tied to anonymous visitors, the caching system may significantly increase the speed of your site.');
+      $output .= '<p>' . t('(For authenticated users, pages need to be assembled for each user individually, but anonymous users all get the exact same version of each page.)') . '</p>';
+      $output .= '</dd>';
+      $output .= '<dt>' . t('Configuring Internal page cache') . '</dt>';
+      $output .= '<dd>';
+      $output .= '<p>' . t('On the <a href="@cache-settings">Performance settings page</a>, you can configure how long browsers and proxies may cache pages, that setting is also respected by the Internal page cache module. There is no other configuration.', array('@cache-settings' => \Drupal::url('system.performance_settings')))  . '</p>';
+      $output .= '</dd>';
+      $output .= '</dl>';
+
+      return $output;
+  }
+}
 
 /**
  * Implements hook_form_alter().
  */
-function page_cache_form_alter(&$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) {
+function page_cache_form_alter(&$form, FormStateInterface $form_state, $form_id) {
   // If the page that's being built is cacheable, set the 'immutable' flag, to
   // ensure that when the form is used, a new form build ID is generated when
   // appropriate, to prevent information disclosure.
   $request_policy = \Drupal::service('page_cache_request_policy');
   $request = \Drupal::requestStack()->getCurrentRequest();
-  $request_is_cacheable = $request_policy->check($request) === \Drupal\Core\PageCache\RequestPolicyInterface::ALLOW;
+  $request_is_cacheable = $request_policy->check($request) === RequestPolicyInterface::ALLOW;
   if ($request_is_cacheable) {
     $form_state->addBuildInfo('immutable', TRUE);
   }
diff --git a/core/modules/page_cache/src/Tests/PageCacheTagsIntegrationTest.php b/core/modules/page_cache/src/Tests/PageCacheTagsIntegrationTest.php
index 1d1b558..996362c 100644
--- a/core/modules/page_cache/src/Tests/PageCacheTagsIntegrationTest.php
+++ b/core/modules/page_cache/src/Tests/PageCacheTagsIntegrationTest.php
@@ -23,6 +23,11 @@ class PageCacheTagsIntegrationTest extends WebTestBase {
 
   protected $profile = 'standard';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['page_cache'];
+
   protected $dumpHeaders = TRUE;
 
   /**
diff --git a/core/modules/system/src/Form/PerformanceForm.php b/core/modules/system/src/Form/PerformanceForm.php
index e4a2de0..e007df9 100644
--- a/core/modules/system/src/Form/PerformanceForm.php
+++ b/core/modules/system/src/Form/PerformanceForm.php
@@ -121,6 +121,7 @@ public function buildForm(array $form, FormStateInterface $form_state) {
       '#type' => 'details',
       '#title' => t('Caching'),
       '#open' => TRUE,
+      '#description' => $this->t('Note: Drupal provides an internal page cache module that is recommended for small to medium-sized websites.'),
     );
     // Identical options to the ones for block caching.
     // @see \Drupal\Core\Block\BlockBase::buildConfigurationForm()
@@ -132,7 +133,7 @@ public function buildForm(array $form, FormStateInterface $form_state) {
       '#title' => t('Page cache maximum age'),
       '#default_value' => $config->get('cache.page.max_age'),
       '#options' => $period,
-      '#description' => t('The maximum time a page can be cached. This is used as the value for max-age in Cache-Control headers.'),
+      '#description' => t('The maximum time a page can be cached by browsers and proxies. This is used as the value for max-age in Cache-Control headers.'),
     );
 
     $directory = 'public://';
diff --git a/core/modules/system/src/Tests/Session/SessionTest.php b/core/modules/system/src/Tests/Session/SessionTest.php
index c5a7220..95eae11 100644
--- a/core/modules/system/src/Tests/Session/SessionTest.php
+++ b/core/modules/system/src/Tests/Session/SessionTest.php
@@ -145,7 +145,6 @@ function testEmptyAnonymousSession() {
 
     // The same behavior is expected when caching is enabled.
     $this->assertTrue($this->container->get('module_installer')->install(['page_cache']), 'Page cache module installed.');
-    $this->rebuildContainer();
     $config = $this->config('system.performance');
     $config->set('cache.page.max_age', 300);
     $config->save();
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 007595e..369e4a2 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -84,7 +84,7 @@ function system_help($route_name, RouteMatchInterface $route_match) {
       $output .= '<dt>' . t('Managing themes') . '</dt>';
       $output .= '<dd>' . t('The System module allows users with the appropriate permissions to install and uninstall themes on the <a href="@themes">Appearance administration page</a>. Themes determine the design and presentation of your site. Drupal comes packaged with several core themes, and additional contributed themes are available at the <a href="@drupal-themes">Drupal.org theme page</a>.', array('@themes' => \Drupal::url('system.themes_page'), '@drupal-themes' => 'http://drupal.org/project/themes')) . '</dd>';
       $output .= '<dt>' . t('Managing caching') . '</dt>';
-      $output .= '<dd>' . t("The System module allows users with the appropriate permissions to manage caching on the <a href='@cache-settings'>Performance settings page</a>. Drupal has a robust caching system that allows the efficient re-use of previously-constructed web pages and web page components. Pages requested by anonymous users are stored in a compressed format; depending on your site configuration and the amount of your web traffic tied to anonymous visitors, the caching system may significantly increase the speed of your site.", array('@cache-settings' => \Drupal::url('system.performance_settings'))) . '</dd>';
+      $output .= '<dd>' . t("The System module allows users with the appropriate permissions to manage caching on the <a href='@cache-settings'>Performance settings page</a>. Drupal has a robust caching system that allows the efficient re-use of previously-constructed web page components.", array('@cache-settings' => \Drupal::url('system.performance_settings'))) . '</dd>';
       $output .= '<dt>' . t('Performing system maintenance') . '</dt>';
       $output .= '<dd>' . t('In order for the site and its modules to continue to operate well, a set of routine administrative operations must run on a regular basis. The System module manages this task by making use of a system cron job. You can verify the status of cron tasks by visiting the <a href="@status">Status report page</a>. For more information, see the online handbook entry for <a href="@handbook">configuring cron jobs</a>. You can set up cron job by visiting <a href="@cron">Cron configuration</a> page', array('@status' => \Drupal::url('system.status'), '@handbook' => 'http://drupal.org/cron', '@cron' => \Drupal::url('system.cron_settings'))) . '</dd>';
       $output .= '<dt>' . t('Configuring basic site settings') . '</dt>';