diff --git a/cache_example/cache_example.routing.yml b/cache_example/cache_example.routing.yml
index 3e38e9d..a35a734 100644
--- a/cache_example/cache_example.routing.yml
+++ b/cache_example/cache_example.routing.yml
@@ -3,4 +3,4 @@ cache_example.description:
   defaults:
     _form: '\Drupal\cache_example\Forms\CacheExampleForm'
   requirements:
-    _access: 'TRUE'
+    _permission: 'access content'
diff --git a/cron_example/cron_example.routing.yml b/cron_example/cron_example.routing.yml
index 677264c..ab824b9 100644
--- a/cron_example/cron_example.routing.yml
+++ b/cron_example/cron_example.routing.yml
@@ -4,4 +4,4 @@ cron_example:
     _form: '\Drupal\cron_example\Form\CronExampleForm'
     _title: 'Cron Example'
   requirements:
-    _access: 'TRUE'
+    _permission: 'access content'
diff --git a/cron_example/src/Tests/CronExampleTestCase.php b/cron_example/src/Tests/CronExampleTestCase.php
index 9511eae..6a15c04 100644
--- a/cron_example/src/Tests/CronExampleTestCase.php
+++ b/cron_example/src/Tests/CronExampleTestCase.php
@@ -37,7 +37,7 @@ class CronExampleTestCase extends WebTestBase {
    *
    * @var array
    */
-  public static $modules = ['cron_example'];
+  public static $modules = ['cron_example', 'node'];
 
   /**
    * {@inheritdoc}
@@ -46,7 +46,7 @@ class CronExampleTestCase extends WebTestBase {
     parent::setUp();
     // Create user. Search content permission granted for the search block to
     // be shown.
-    $this->drupalLogin($this->drupalCreateUser(['administer site configuration']));
+    $this->drupalLogin($this->drupalCreateUser(['administer site configuration', 'access content']));
 
     $this->cronConfig = \Drupal::configFactory()->getEditable('examples.cron');
   }
diff --git a/dbtng_example/dbtng_example.routing.yml b/dbtng_example/dbtng_example.routing.yml
index 81fc5ee..56baf53 100644
--- a/dbtng_example/dbtng_example.routing.yml
+++ b/dbtng_example/dbtng_example.routing.yml
@@ -4,7 +4,7 @@ dbtng_example:
     _title: 'DBTNG Example'
     _controller: '\Drupal\dbtng_example\DBTNGExampleController::entryList'
   requirements:
-    _access: 'TRUE'
+    _permission: 'access content'
 
 dbtng_list:
   path: 'examples/dbtng_example/list'
@@ -12,7 +12,7 @@ dbtng_list:
     _title: 'List'
     _controller: '\Drupal\dbtng_example\DBTNGExampleController::entryList'
   requirements:
-    _access: 'TRUE'
+    _permission: 'access content'
 
 dbtng_add:
   path: 'examples/dbtng_example/add'
@@ -20,7 +20,7 @@ dbtng_add:
     _title: 'Add Entry'
     _form: '\Drupal\dbtng_example\DBTNGExampleAddForm'
   requirements:
-    _access: 'TRUE'
+    _permission: 'access content'
 
 dbtng_update:
   path: 'examples/dbtng_example/update'
@@ -28,7 +28,7 @@ dbtng_update:
     _title: 'Update Entry'
     _form: '\Drupal\dbtng_example\DBTNGExampleUpdateForm'
   requirements:
-    _access: 'TRUE'
+    _permission: 'access content'
 
 dbtng_advanced:
   path: 'examples/dbtng_example/advanced'
@@ -36,4 +36,4 @@ dbtng_advanced:
     _title: 'Advanced List'
     _controller: '\Drupal\dbtng_example\DBTNGExampleController::entryAdvancedList'
   requirements:
-    _access: 'TRUE'
+    _permission: 'access content'
diff --git a/email_example/email_example.routing.yml b/email_example/email_example.routing.yml
index 2701dad..7e329f4 100644
--- a/email_example/email_example.routing.yml
+++ b/email_example/email_example.routing.yml
@@ -3,4 +3,4 @@ email_example.description:
   defaults:
     _form: '\Drupal\email_example\Form\EmailExampleGetFormPage'
   requirements:
-    _access: 'TRUE'
+    _permission: 'access content'
diff --git a/examples.module b/examples.module
index c60f841..abc53b7 100644
--- a/examples.module
+++ b/examples.module
@@ -45,6 +45,7 @@ function examples_toolbar() {
     'node_type_example' => 'config_node_type_example.description',
     'page_example' => 'page_example_description',
     'phpunit_example' => 'phpunit_example_description',
+    'plugin_type_example' => 'plugin_type_example.description',
     'simpletest_example' => 'simpletest_example_description',
     'session_example' => 'session_example.form',
     'tour_example' => 'tour_example_description',
diff --git a/field_example/field_example.routing.yml b/field_example/field_example.routing.yml
index 86efe8c..3d600e1 100644
--- a/field_example/field_example.routing.yml
+++ b/field_example/field_example.routing.yml
@@ -4,4 +4,4 @@ field_example.description:
   defaults:
     _controller: '\Drupal\field_example\Controller\FieldExampleController::description'
   requirements:
-    _access: 'TRUE'
+    _permission: 'access content'
diff --git a/js_example/js_example.routing.yml b/js_example/js_example.routing.yml
index 603e5df..ba86225 100755
--- a/js_example/js_example.routing.yml
+++ b/js_example/js_example.routing.yml
@@ -4,7 +4,7 @@ js_example.info:
     _title: 'JavaScript Example Information'
     _controller: '\Drupal\js_example\Controller\JsExampleController::info'
   requirements:
-    _access: 'TRUE'
+    _permission: 'access content'
 
 js_example.weights:
   path: '/examples/js_example/weights'
@@ -12,7 +12,7 @@ js_example.weights:
     _title: 'JS Example: see weighting in action'
     _controller: '\Drupal\js_example\Controller\JsExampleController::getJsWeightImplementation'
   requirements:
-    _access: 'TRUE'
+    _permission: 'access content'
 
 js_example.accordion:
   path: '/examples/js_example/accordion'
@@ -20,4 +20,4 @@ js_example.accordion:
     _title: 'JS Example: jQuery UI accordion'
     _controller: '\Drupal\js_example\Controller\JsExampleController::getJsAccordionImplementation'
   requirements:
-    _access: 'TRUE'
+    _permission: 'access content'
diff --git a/js_example/src/Tests/JsExampleTest.php b/js_example/src/Tests/JsExampleTest.php
index a172e19..da003e5 100644
--- a/js_example/src/Tests/JsExampleTest.php
+++ b/js_example/src/Tests/JsExampleTest.php
@@ -23,17 +23,17 @@ class JsExampleTest extends WebTestBase {
    *
    * @var array
    */
-  public static $modules = array('js_example');
+  public static $modules = array('js_example', 'node');
 
   /**
    * Test all the paths defined by our module.
    */
   public function testJsExample() {
-    $paths = array(
+    $paths = [
       'examples/js_example',
       'examples/js_example/weights',
       'examples/js_example/accordion',
-    );
+    ];
     foreach ($paths as $path) {
       $this->drupalGet($path);
       $this->assertResponse(200, 'Visited ' . $path);
diff --git a/node_type_example/node_type_example.routing.yml b/node_type_example/node_type_example.routing.yml
index 6c31bdb..e3483e9 100644
--- a/node_type_example/node_type_example.routing.yml
+++ b/node_type_example/node_type_example.routing.yml
@@ -3,4 +3,4 @@ config_node_type_example.description:
   defaults:
     _controller: '\Drupal\node_type_example\Controller\NodeTypeExampleController::description'
   requirements:
-    _access: 'TRUE'
+    _permission: 'access content'
diff --git a/page_example/page_example.routing.yml b/page_example/page_example.routing.yml
index 5c970a1..e207227 100644
--- a/page_example/page_example.routing.yml
+++ b/page_example/page_example.routing.yml
@@ -20,7 +20,7 @@ page_example_description:
     _controller: '\Drupal\page_example\Controller\PageExampleController::description'
     _title: 'Page Example'
   requirements:
-    _access: 'TRUE'
+    _permission: 'access content'
 
 # If the user accesses http://example.com/?q=examples/page_example/simple,
 # the routing system will look for a route with that path. In this case it will
diff --git a/phpunit_example/phpunit_example.routing.yml b/phpunit_example/phpunit_example.routing.yml
index d7c3fbc..51f8e2d 100644
--- a/phpunit_example/phpunit_example.routing.yml
+++ b/phpunit_example/phpunit_example.routing.yml
@@ -5,4 +5,4 @@ phpunit_example_description:
   defaults:
     _controller: '\Drupal\phpunit_example\Controller\PHPUnitExampleController::description'
   requirements:
-    _access: 'TRUE'
+    _permission: 'access content'
diff --git a/plugin_type_example/plugin_type_example.api.php b/plugin_type_example/plugin_type_example.api.php
new file mode 100644
index 0000000..8ad888c
--- /dev/null
+++ b/plugin_type_example/plugin_type_example.api.php
@@ -0,0 +1,23 @@
+<?php
+/**
+ * @file
+ * Hooks specific to the plugin_type_example module.
+ */
+
+/**
+ * Alter the definitions of all the Sandwich plugins.
+ *
+ * You can implement this hook to do things like change the properties for each
+ * plugin or change the implementing class for a plugin.
+ *
+ * This hook is invoked by SandwichPluginManager::__construct().
+ *
+ * @param array $sandwich_plugin_info
+ *   This is the array of plugin definitions.
+ */
+function hook_sandwich_info_alter(array $sandwich_plugin_info) {
+  // Let's change the 'foobar' property for all sandwiches.
+  foreach ($sandwich_plugin_info as $plugin_id => $plugin_definition) {
+    $sandwich_plugin_info[$plugin_id]['foobar'] = t('We have altered this in the alter hook');
+  }
+}
diff --git a/plugin_type_example/plugin_type_example.info.yml b/plugin_type_example/plugin_type_example.info.yml
new file mode 100644
index 0000000..5777402
--- /dev/null
+++ b/plugin_type_example/plugin_type_example.info.yml
@@ -0,0 +1,7 @@
+name: Plugin type example
+type: module
+description: Provides an example of defining a plugin type.
+package: Example modules
+core: 8.x
+dependencies:
+  - examples
diff --git a/plugin_type_example/plugin_type_example.links.menu.yml b/plugin_type_example/plugin_type_example.links.menu.yml
new file mode 100644
index 0000000..c607e36
--- /dev/null
+++ b/plugin_type_example/plugin_type_example.links.menu.yml
@@ -0,0 +1,3 @@
+plugin_type_example.description:
+  title: Plugin Type Example
+  route_name: plugin_type_example.description
diff --git a/plugin_type_example/plugin_type_example.module b/plugin_type_example/plugin_type_example.module
new file mode 100644
index 0000000..73855c9
--- /dev/null
+++ b/plugin_type_example/plugin_type_example.module
@@ -0,0 +1,55 @@
+<?php
+
+/**
+ * @file
+ * Demonstrates how to define a new plugin type.
+ */
+
+/**
+ * @defgroup plugin_type_example Example: Plugin Types
+ * @ingroup examples
+ * @{
+ * Example of how to define a plugin type.
+ *
+ * Our example defines a Sandwich plugin type.  Sandwich's come in many flavors,
+ * each having their unique qualities, but also sharing things in common.  Our
+ * Sandwich plugins will be very simple, each providing a unique description
+ * or themselves.  Sandwich plugins also have an id and a property called
+ * foobar, which we'll use to demonstrate how you can alter a plugin using an
+ * alter hook.
+ *
+ * Start at the class \Drupal\plugin_type_example\SandwichPluginManager, which
+ * defines our plugin type manager.  Our plugin type manager is exposed to
+ * Drupal as a service in the plugin_type_example.services.yml file.
+ *
+ * We've also defined two implementations of our plugin type,
+ * \Drupal\plugin_type_example\Plugin\Sandwich\ExampleHamSandwich and
+ * \Drupal\plugin_type_example\Plugin\Sandwich\ExampleMeatballSandwich. Take a
+ * look at each.  These plugins use annotated plugin discovery, and as such have
+ * an annotation block in the doc block for the class.  Other than that, they
+ * implement the \Drupal\plugin_type_example\SandwichInterface, which is
+ * required, since we've set that interface for the plugin type in
+ * \Drupal\plugin_type_example\SandwichPluginManager::__construct.
+ *
+ * To see the plugins in action visit /examples/plugin_type_example.  The output
+ * is rendered in
+ * Drupal\plugin_type_example\Controller\PluginTypeExampleController::description().
+ * Read through that method to see how to use plugins using the
+ * plugin.manager.sandwich service.
+ */
+
+/**
+ * Implements hook_sandwich_info_alter().
+ */
+function plugin_type_example_sandwich_info_alter(&$sandwich_plugin_info) {
+  // Let's change the 'foobar' property for all sandwiches.
+  foreach ($sandwich_plugin_info as $plugin_id => $plugin_definition) {
+    $sandwich_plugin_info[$plugin_id]['foobar'] = t('We have altered this in the alter hook');
+  }
+
+  // The ham sandwich is more calorific in our system.  Note that the string
+  // 'ham_sandwich' is the id name of the Ham Sandwich plugin, which is set
+  // in the annotation in
+  // \Drupal\plugin_type_example\Plugin\Sandwich\ExampleHamSandwich
+  $sandwich_plugin_info['ham_sandwich']['calories'] = 500;
+}
diff --git a/plugin_type_example/plugin_type_example.routing.yml b/plugin_type_example/plugin_type_example.routing.yml
new file mode 100644
index 0000000..20b32ef
--- /dev/null
+++ b/plugin_type_example/plugin_type_example.routing.yml
@@ -0,0 +1,8 @@
+# This defines our example page's path to the routing system.
+plugin_type_example.description:
+  path: '/examples/plugin_type_example'
+  defaults:
+    _controller: '\Drupal\plugin_type_example\Controller\PluginTypeExampleController::description'
+    _title: 'Plugin Type Example'
+  requirements:
+    _permission: 'access content'
diff --git a/plugin_type_example/plugin_type_example.services.yml b/plugin_type_example/plugin_type_example.services.yml
new file mode 100644
index 0000000..bd9c129
--- /dev/null
+++ b/plugin_type_example/plugin_type_example.services.yml
@@ -0,0 +1,19 @@
+# This declares the plugin manager to the service container.
+# For background information on the service container, see
+# http://symfony.com/doc/current/book/service_container.html.
+# Services declaration files such as this one are compiled to PHP code in
+# sites/default/files/php/service_container, so changes here require that folder
+# to be deleted in order to have Drupal notice them.
+services:
+  # The machine name of the service. This is the string that must be passed to
+  # Drupal::service() to get the instantiated plugin manager.
+  plugin.manager.sandwich:
+    # This tells the service container the name of our plugin manager class.
+    class: Drupal\plugin_type_example\SandwichPluginManager
+    # The default parameters to pass to the class constructor,
+    # SandwichPluginManager::__construct().
+    # Arguments beginning with @ are the names of other services that are being
+    # injected into this service. Many common ones are found in
+    # /core/core.services.yml.
+    # See https://drupal.org/node/2133171 for more detail.
+    arguments: ['@container.namespaces', '@cache.default', '@module_handler']
diff --git a/plugin_type_example/src/Controller/PluginTypeExampleController.php b/plugin_type_example/src/Controller/PluginTypeExampleController.php
new file mode 100644
index 0000000..477c638
--- /dev/null
+++ b/plugin_type_example/src/Controller/PluginTypeExampleController.php
@@ -0,0 +1,129 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\plugin_type_example\Controller\PluginTypeExampleController.
+ */
+
+namespace Drupal\plugin_type_example\Controller;
+
+use Drupal\Core\Controller\ControllerBase;
+use Drupal\plugin_type_example\SandwichPluginManager;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Controller for our example pages.
+ */
+class PluginTypeExampleController extends ControllerBase {
+
+  /**
+   * The sandwich plugin manager.
+   *
+   * We use this to get all of the sandwich plugins.
+   *
+   * @var \Drupal\plugin_type_example\SandwichPluginManager
+   */
+  protected $sandwichManager;
+
+  /**
+   * Constructor.
+   *
+   * @param \Drupal\plugin_type_example\SandwichPluginManager $sandwich_manager
+   *   The sandwich plugin manager service. We're injecting this service so that
+   *   we can use it to access the sandwich plugins.
+   */
+  public function __construct(SandwichPluginManager $sandwich_manager) {
+    $this->sandwichManager = $sandwich_manager;
+  }
+
+  /**
+   * Displays a page with an overview of our plugin type and plugins.
+   *
+   * Lists all the Sandwich plugin definitions by using methods on the
+   * \Drupal\plugin_type_example\SandwichPluginManager class.  Lists out the
+   * description for each plugin found by invoking methods defined on the
+   * plugins themselves.  You can find the plugins we have defined in the
+   * \Drupal\plugin_type_example\Plugin\Sandwich namespace.
+   */
+  public function description() {
+    $build = array();
+
+    $build['intro'] = array(
+      '#markup' => t("This page lists the sandwich plugins we've created. The sandwich plugin type is defined in Drupal\\plugin_type_example\\SandwichPluginManager. The various plugins are defined in the Drupal\\plugin_type_example\\Plugin\\Sandwich namespace."),
+    );
+
+    // Get the list of all the sandwich plugins defined on the system from the
+    // plugin manager.
+    // Note that at this point, what we have is *definitions* of plugins, not
+    // the plugins themselves.
+    $sandwich_plugin_definitions = $this->sandwichManager->getDefinitions();
+
+    // Let's output a list of the plugin definitions we now have.
+    $items = array();
+    foreach ($sandwich_plugin_definitions as $sandwich_plugin_definition) {
+      // Here we use various properties from the plugin definition. These values
+      // are defined in the annotation at the top of the plugin class: see
+      // ExampleHamSandwich.
+      $items[] = t("!id (calories: !calories, foobar: !foobar )", array(
+        '!id'       => $sandwich_plugin_definition['id'],
+        '!calories' => $sandwich_plugin_definition['calories'],
+        '!foobar'   => $sandwich_plugin_definition['foobar'],
+      ));
+    }
+
+    // Add our list to the render array.
+    $build['plugin_definitions'] = array(
+      '#theme' => 'item_list',
+      '#title' => 'Sandwich plugin definitions',
+      '#items' => $items,
+    );
+
+    // If we want just a single plugin definition, we can use getDefinition().
+    // This requires us to know the ID of the plugin we want. This is set in the
+    // annotation on the plugin class: see ExampleHamSandwich.
+    $ham_sandwich_plugin_definition = $this->sandwichManager->getDefinition('ham_sandwich');
+
+    // To get an actual plugin, we call createInstance() on the plugin manager,
+    // passing the ID of the plugin we want to load. Let's output a list of the
+    // actual plugins.
+    $items = array();
+    // The array of plugin definitions is keyed by plugin id, so we can just use
+    // that to load our plugins.
+    foreach ($sandwich_plugin_definitions as $plugin_id => $sandwich_plugin_definition) {
+      // We now have a plugin! From here on it can be treated just as any other
+      // object: have its properties examined, methods called, etc.
+      $plugin = $this->sandwichManager->createInstance($plugin_id, array('of' => 'configuration values'));
+      $items[] = $plugin->description();
+    }
+
+    $build['plugins'] = array(
+      '#theme' => 'item_list',
+      '#title' => 'Sandwich plugins',
+      '#items' => $items,
+    );
+
+    return $build;
+  }
+
+  /**
+   * {@inheritdoc}
+   *
+   * Override the parent method so that we can inject out sandwich plugin
+   * manager service into the controller.  This is dependancy injection at work
+   * for a controller.  Rather than access the global service container via
+   * \Drupal::service(), it's best practice to use dependancy injection.  Notice
+   * our controller extends ControllerBase, which implements the
+   * ContainerInjectionInterface interface.  As such we can implement a create
+   * method to control how our controller in instantiated.  We do just that,
+   * passing in the sandwich plugin manager service that we need.
+   */
+  public static function create(ContainerInterface $container) {
+    // Use the service container to instantiate a new instance of our
+    // controller.  The string we pass is the machine name of the service,
+    // which is set in the plugin_type_example.services.yml file.  We get back
+    // an instance of our SandwichPluginManager class, which is passed to the
+    // controller's constructor.
+    return new static($container->get('plugin.manager.sandwich'));
+  }
+
+}
diff --git a/plugin_type_example/src/Plugin/Sandwich/ExampleHamSandwich.php b/plugin_type_example/src/Plugin/Sandwich/ExampleHamSandwich.php
new file mode 100644
index 0000000..1c6df09
--- /dev/null
+++ b/plugin_type_example/src/Plugin/Sandwich/ExampleHamSandwich.php
@@ -0,0 +1,48 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\plugin_type_example\Plugin\Sandwich\ExampleHamSandwich.
+ */
+
+namespace Drupal\plugin_type_example\Plugin\Sandwich;
+
+use Drupal\Core\Plugin\PluginBase;
+use Drupal\plugin_type_example\SandwichInterface;
+
+/**
+ * Provides a ham sandwich.
+ *
+ * Because the plugin manager class for our plugins uses annotated class
+ * discovery, our ham sandwich only needs to exist within the Plugin\Sandwich
+ * namespace to be declared as a plugin. This is defined in
+ * \Drupal\plugin_type_example\SandwichPluginManager::__construct().
+ *
+ * The following is the plugin annotation. This is parsed by Doctrine to make
+ * the plugin definition. Any values defined here will be available in the
+ * plugin definition.
+ *
+ * This should be used for metadata that is specifically required to instantiate
+ * the plugin, or for example data that might be needed to display a list of all
+ * available plugins where the user selects one. This means many plugin
+ * annotations can be reduced to a plugin ID, a label and perhaps a description.
+ *
+ * @Plugin(
+ *   id = "ham_sandwich",
+ *   foobar = @Translation("This is an example value that is defined in the annotation."),
+ *   calories = 426,
+ * )
+ */
+class ExampleHamSandwich extends PluginBase implements SandwichInterface {
+
+  /**
+   * Get a description of the sandwich fillings.
+   *
+   * This is just an example method on our plugin that we can call to get
+   * something back.
+   */
+  public function description() {
+    return $this->t('Ham, mustard, rocket, sun-dried tomatoes.');
+  }
+
+}
diff --git a/plugin_type_example/src/Plugin/Sandwich/ExampleMeatballSandwich.php b/plugin_type_example/src/Plugin/Sandwich/ExampleMeatballSandwich.php
new file mode 100644
index 0000000..592ed07
--- /dev/null
+++ b/plugin_type_example/src/Plugin/Sandwich/ExampleMeatballSandwich.php
@@ -0,0 +1,48 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\plugin_type_example\Plugin\Sandwich\ExampleMeatballSandwich.
+ */
+
+namespace Drupal\plugin_type_example\Plugin\Sandwich;
+
+use Drupal\Core\Plugin\PluginBase;
+use Drupal\plugin_type_example\SandwichInterface;
+
+/**
+ * Provides a meatball sandwich.
+ *
+ * Because the plugin manager class for our plugins uses annotated class
+ * discovery, our meatball sandwich only needs to exist within the
+ * Plugin\Sandwich namespace to be declared as a plugin. This is defined in
+ * \Drupal\plugin_type_example\SandwichPluginManager::__construct().
+ *
+ * The following is the plugin annotation. This is parsed by Doctrine to make
+ * the plugin definition. Any values defined here will be available in the
+ * plugin definition.
+ *
+ * This should be used for metadata that is specifically required to instantiate
+ * the plugin, or for example data that might be needed to display a list of all
+ * available plugins where the user selects one. This means many plugin
+ * annotations can be reduced to a plugin ID, a label and perhaps a description.
+ *
+ * @Plugin(
+ *   id = "meatball_sandwich",
+ *   foobar = @Translation("Right around that corner there is a sandwich shop. They sell meatball sandwiches, the best I ever tasted. Would you go get me two? Come on partner. Thank you. Utah! Get me two!"),
+ *   calories = 1200,
+ * )
+ */
+class ExampleMeatballSandwich extends PluginBase implements SandwichInterface {
+
+  /**
+   * Get a description of the sandwich fillings.
+   *
+   * This is just an example method on our plugin that we can call to get
+   * something back.
+   */
+  public function description() {
+    return $this->t('Enjoy Italian style meatballs drenched in irresistible marinara sauce, served on freshly baked bread.');
+  }
+
+}
diff --git a/plugin_type_example/src/SandwichInterface.php b/plugin_type_example/src/SandwichInterface.php
new file mode 100644
index 0000000..f1c7187
--- /dev/null
+++ b/plugin_type_example/src/SandwichInterface.php
@@ -0,0 +1,22 @@
+<?php
+/**
+ * @file
+ * Provides Drupal\plugin_type_example\SandwichInterface.
+ */
+
+namespace Drupal\plugin_type_example;
+
+/**
+ * An interface for all Sandwich type plugins.
+ */
+interface SandwichInterface {
+
+  /**
+   * Provide a description of the sandwich.
+   *
+   * @return string
+   *   A string description of the sandwich.
+   */
+  public function description();
+
+}
diff --git a/plugin_type_example/src/SandwichPluginManager.php b/plugin_type_example/src/SandwichPluginManager.php
new file mode 100644
index 0000000..c423ecb
--- /dev/null
+++ b/plugin_type_example/src/SandwichPluginManager.php
@@ -0,0 +1,70 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\plugin_type_example\SandwichPluginManager.
+ */
+
+namespace Drupal\plugin_type_example;
+
+use Drupal\Core\Cache\CacheBackendInterface;
+use Drupal\Core\Extension\ModuleHandlerInterface;
+use Drupal\Core\Plugin\DefaultPluginManager;
+
+/**
+ * Manages sandwich plugins.
+ *
+ * The SandwichPluginManager class extends the DefaultPluginManager to provide
+ * a way to manage sandwich plugins.
+ *
+ * As well as this class definition, we need to declare our plugin manager class
+ * as a service, in the plugin_type_example.services.yml file.
+ */
+class SandwichPluginManager extends DefaultPluginManager {
+
+  /**
+   * Creates the discovery object.
+   *
+   * @param \Traversable $namespaces
+   *   An object that implements \Traversable which contains the root paths
+   *   keyed by the corresponding namespace to look for plugin implementations.
+   * @param \Drupal\Core\Cache\CacheBackendInterface $cache_backend
+   *   Cache backend instance to use.
+   * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
+   *   The module handler to invoke the alter hook with.
+   */
+  public function __construct(\Traversable $namespaces, CacheBackendInterface $cache_backend, ModuleHandlerInterface $module_handler) {
+    // We replace the $subdir parameter with our own value.
+    // This tells the plugin system to look for plugins in the 'Plugin/Sandwich'
+    // subfolder inside modules' 'src' folder.
+    $subdir = 'Plugin/Sandwich';
+
+    // The name of the interface that plugins should adhere to.  Drupal will
+    // enforce this as a requirement.  If a plugin does not implement this
+    // interface, than Drupal will throw an error.
+    $plugin_interface = 'Drupal\plugin_type_example\SandwichInterface';
+
+    // The name of the annotation class that contains the plugin definition.
+    $plugin_definition_annotation_name = 'Drupal\Component\Annotation\Plugin';
+
+    parent::__construct($subdir, $namespaces, $module_handler, $plugin_interface, $plugin_definition_annotation_name);
+
+    // This allows the plugin definitions to be altered by an alter hook. The
+    // parameter defines the name of the hook, thus: hook_sandwich_info_alter().
+    // In this example, we implement this hook to change the plugin definitions:
+    // see plugin_type_example_sandwich_info_alter().
+    $this->alterInfo('sandwich_info');
+
+    // This sets the caching method for our plugin definitions.  Plugin
+    // definitions are cached using the provided cache backend.  For our
+    // Sandwich plugin type, we've specified the @cache.default service be used
+    // in the plugin_type_example.services.yml file.  The second argument is a
+    // cache key prefix.  Out of the box Drupal with the default cache backend
+    // setup will store our plugin definition in the cache_default table using
+    // the sandwich_info key.  All that is implementation details however,
+    // all we care about it that caching for our plugin definition is taken
+    // care of by this call.
+    $this->setCacheBackend($cache_backend, 'sandwich_info');
+  }
+
+}
diff --git a/plugin_type_example/src/Tests/PluginTypeExampleTest.php b/plugin_type_example/src/Tests/PluginTypeExampleTest.php
new file mode 100644
index 0000000..1cc5e9a
--- /dev/null
+++ b/plugin_type_example/src/Tests/PluginTypeExampleTest.php
@@ -0,0 +1,77 @@
+<?php
+
+/**
+ * @file
+ * Test case for Testing the page example module.
+ *
+ * This file contains the test cases to check if module is performing as
+ * expected.
+ */
+
+namespace Drupal\plugin_type_example\Tests;
+
+use Drupal\simpletest\WebTestBase;
+
+/**
+ * Test the functionality of the Plugin Type Example module.
+ *
+ * @ingroup plugin_type_example
+ *
+ * @group plugin_type_example
+ * @group examples
+ */
+class PluginTypeExampleTest extends WebTestBase {
+
+  /**
+   * Modules to enable.
+   *
+   * @var array
+   */
+  public static $modules = array('plugin_type_example');
+
+  /**
+   * The installation profile to use with this test.
+   *
+   * @var string
+   */
+  protected $profile = 'minimal';
+
+  /**
+   * Test the plugin manager can be loaded, and the plugins are registered.
+   */
+  public function testPluginExample() {
+    $manager = \Drupal::service('plugin.manager.sandwich');
+
+    $sandwich_plugin_definitions = $manager->getDefinitions();
+
+    // Check we have only one sandwich plugin.
+    $this->assertEqual(count($sandwich_plugin_definitions), 2, 'There are two sandwich plugins defined.');
+
+    // Check some of the properties of the ham sandwich plugin definition.
+    $sandwich_plugin_definition = $sandwich_plugin_definitions['ham_sandwich'];
+    $this->assertEqual($sandwich_plugin_definition['calories'], 500, 'The ham sandwich plugin definition\'s calories property is set.');
+
+    // Check the alter hook fired and changed a property.
+    $this->assertEqual($sandwich_plugin_definition['foobar'], 'We have altered this in the alter hook', 'The ham sandwich plugin definition\'s foobar property is set, and was correctly altered by the plugin info alter hook.');
+
+    // Create an instance of the ham sandwich plugin to check it works.
+    $plugin = $manager->createInstance('ham_sandwich', array('of' => 'configuration values'));
+
+    $this->assertEqual(get_class($plugin), 'Drupal\plugin_type_example\Plugin\Sandwich\ExampleHamSandwich', 'The ham sandwich plugin is instantiated and of the correct class.');
+  }
+
+  /**
+   * Test the output of the example page.
+   */
+  public function testPluginExamplePage() {
+    $this->drupalGet('examples/plugin_type_example');
+    $this->assertResponse(200, 'Example page successfully accessed.');
+
+    // Check we see the plugin id.
+    $this->assertText(t('ham_sandwich'), 'The plugin ID is output.');
+
+    // Check we see the plugin description.
+    $this->assertText(t('Ham, mustard, rocket, sun-dried tomatoes.'), 'The plugin description is output.');
+  }
+
+}
diff --git a/session_example/session_example.routing.yml b/session_example/session_example.routing.yml
index a67fde4..da22c65 100644
--- a/session_example/session_example.routing.yml
+++ b/session_example/session_example.routing.yml
@@ -11,6 +11,7 @@ session_example.view:
   path: '/examples/session_example/view'
   defaults:
     _controller: '\Drupal\session_example\Controller\SessionExampleController::showSession'
+    _title: 'Session Example: Current Values'
   requirements:
     _access: 'TRUE'
   options:
diff --git a/session_example/src/Controller/SessionExampleController.php b/session_example/src/Controller/SessionExampleController.php
index 83da33a..3bb4b28 100644
--- a/session_example/src/Controller/SessionExampleController.php
+++ b/session_example/src/Controller/SessionExampleController.php
@@ -25,8 +25,17 @@ class SessionExampleController extends ControllerBase {
     $session = $request->getSession();
     $name = $session->get('session_example.name', $this->t('No Name'));
     $email = $session->get('session_example.email', $this->t('No EMail'));
+    $quest = $session->get('session_example.quest', $this->t('No Quest'));
+    $color = $session->get('session_example.color', $this->t('No Color'));
     return [
-      '#markup' => $this->t('Name: @name, EMail: @email', ['@name' => $name, '@email' => $email]),
+      'description' => [
+        '#type' => 'item',
+        '#title' => $this->t('Saved Session Keys'),
+        '#markup' => $this->t('The example form lets you set some session keys.  This page lists what their current values are.'),
+      ],
+      'session_status' => [
+        '#markup' => $this->t('Name: @name, EMail: @email,  Quest: @quest, Color: @color', ['@name' => $name, '@email' => $email, '@quest' => $quest, '@color' => $color]),
+      ],
       '#cache' => [
       'max-age' => 0,
       ]
diff --git a/session_example/src/Form/SessionExampleForm.php b/session_example/src/Form/SessionExampleForm.php
index 7403d37..022f68f 100644
--- a/session_example/src/Form/SessionExampleForm.php
+++ b/session_example/src/Form/SessionExampleForm.php
@@ -76,15 +76,41 @@ class SessionExampleForm extends FormBase {
    */
   public function buildForm(array $form, FormStateInterface $form_state) {
     $session = $this->getExampleSession();
+    $form['description'] = [
+      '#type' => 'item',
+      '#title' => $this->t('Session Data Test Form'),
+      '#markup' => $this->t('In this example form, data that you enter into the form will be saved into your session data, which persists until you log out of Drupal.'),
+    ];
     $form['name'] = [
       '#type' => 'textfield',
       '#title' => $this->t('Name'),
-      '#default_value' => $session->get('session_example.name', 'My Name'),
+      '#placeholder' => $this->t('Your name.'),
+      '#default_value' => $session->get('session_example.name', ''),
     ];
     $form['email'] = [
       '#type' => 'textfield',
       '#title' => $this->t('Email'),
-      '#default_value' => $session->get('session_example.email', 'My Email'),
+      '#placeholder' => $this->t('Your email address.'),
+      '#default_value' => $session->get('session_example.email', ''),
+    ];
+    $form['quest'] = [
+      '#type' => 'textfield',
+      '#title' => $this->t('Quest'),
+      '#placeholder' => $this->t('What is your quest?'),
+      '#default_value' => $session->get('session_example.quest', ''),
+    ];
+    $form['color'] = [
+      '#type' => 'select',
+      '#title' => $this->t('Favorite Color'),
+      '#options' => [
+        '' => $this->t('--'),
+        'red' => $this->t('Red'),
+        'blue' => $this->t('Blue'),
+        'yellow' => $this->t('Yellow'),
+        'argggh' => $this->t('Argggghhh!!'),
+      ],
+      '#default_value' => $session->get('session_example.color', ''),
+      '#description' => $this->t('What is your favorite color?'),
     ];
     $form['save'] = [
       '#type' => 'submit',
@@ -102,20 +128,34 @@ class SessionExampleForm extends FormBase {
    * {@inheritdoc}
    */
   public function submitForm(array &$form, FormStateInterface $form_state) {
-    $session = $this->getExampleSession();
-    $session->set('session_example.name', $form_state->getValue('name'));
-    $session->set('session_example.email', $form_state->getValue('email'));
+    $this->setSessionKeyIfChanged('session_example.name', $form_state->getValue('name'));
+    $this->setSessionKeyIfChanged('session_example.email', $form_state->getValue('email'));
+    $this->setSessionKeyIfChanged('session_example.quest', $form_state->getValue('quest'));
+    $this->setSessionKeyIfChanged('session_example.color', $form_state->getValue('color'));
     $link = $this->link_generator->generate($this->t('Check here'), Url::fromRoute('session_example.view'));
     drupal_set_message($this->t('The session has been saved successfully. @link', ['@link' => $link]));
   }
 
   /**
+   * Since we're using placeholders, do not write over an empty session key for an empty field.
+   */
+  protected function setSessionKeyIfChanged($key, $value) {
+    $session = $this->getExampleSession();
+    $old = $session->get($key, '');
+    if ($value !== $old) {
+      $session->set($key, $value);
+    }
+  }
+
+  /**
    * Clears the name and email session.
    */
   public function submitClearSession(array &$form, FormStateInterface $form_state) {
     $session = $this->getExampleSession();
     $session->remove('session_example.name');
     $session->remove('session_example.email');
+    $session->remove('session_example.quest');
+    $session->remove('session_example.color');
     drupal_set_message($this->t('Session is cleared.'));
   }
 }
diff --git a/session_example/src/Tests/SessionExampleTest.php b/session_example/src/Tests/SessionExampleTest.php
index f69a49b..9f5b9e9 100644
--- a/session_example/src/Tests/SessionExampleTest.php
+++ b/session_example/src/Tests/SessionExampleTest.php
@@ -8,6 +8,7 @@
 namespace Drupal\session_example\Tests;
 
 use Drupal\simpletest\WebTestBase;
+use Drupal\block\Tests\BlockTestBase;
 
 /**
  * Tests the basic functions of the Session Example module.
@@ -27,17 +28,22 @@ class SessionExampleTest extends WebTestBase {
    */
   public function testSessionExample() {
 
+    $this->drupalPlaceBlock('local_tasks_block', array('region' => 'content'));
     $this->drupalPlaceBlock('system_menu_block:tools', array());
     $this->drupalGet('');
     $this->assertLink(t('Session Example'));
 
+
     $this->clickLink(t('Session Example'));
-    $this->assertFieldByName('name', 'My Name', 'Name Field contains My Name');
-    $this->assertFieldByName('email', 'My Email', 'Email Field contains My Email');
+    $this->assertRaw('placeholder="Your name."', 'Name placeholder contains Your name');
+    $this->assertRaw('placeholder="Your email address."', 'Email placeholder contains Your email address.');
+    $this->assertRaw('placeholder="What is your quest?"', 'Name placeholder contains What is your quest?');
 
     $this->clickLink(t('View'));
     $this->assertText('No Name');
     $this->assertText('No EMail');
+    $this->assertText('No Quest');
+    $this->assertText('No Color');
 
     $this->clickLink(t('Form'));
     $this->drupalPostForm(NULL, array(), t('Save'));
@@ -45,8 +51,23 @@ class SessionExampleTest extends WebTestBase {
     $this->assertLink(t('Check here'));
 
     $this->clickLink(t('Check here'));
-    $this->assertText('My Name');
-    $this->assertText('My Email');
+    $this->assertText('No Name');
+    $this->assertText('No EMail');
+    $this->assertText('No Quest');
+    $this->assertText('No Color');
+
+    $form_data = [
+      'name' => 'Sir Lancelot',
+      'quest' => 'To seek the Grail',
+      'color'  => 'blue',
+    ];
+    $this->clickLink(t('Form'));
+    $this->drupalPostForm(NULL, $form_data, t('Save'));
+
+    $this->clickLink(t('Check here'));
+    $this->assertText('Sir Lancelot');
+    $this->assertText('To seek the Grail');
+    $this->assertText('blue');
 
     $this->clickLink(t('Form'));
     $this->drupalPostForm(NULL, array(), t('Clear Session'));
@@ -57,4 +78,5 @@ class SessionExampleTest extends WebTestBase {
     $this->assertText('No EMail');
 
   }
+
 }
diff --git a/simpletest_example/simpletest_example.routing.yml b/simpletest_example/simpletest_example.routing.yml
index 90f5822..c8a9318 100644
--- a/simpletest_example/simpletest_example.routing.yml
+++ b/simpletest_example/simpletest_example.routing.yml
@@ -5,4 +5,4 @@ simpletest_example_description:
   defaults:
     _controller: '\Drupal\simpletest_example\Controller\SimpleTestExampleController::description'
   requirements:
-    _access: 'TRUE'
+    _permission: 'access content'
diff --git a/tablesort_example/tablesort_example.routing.yml b/tablesort_example/tablesort_example.routing.yml
index 2fa88cd..1f232e6 100644
--- a/tablesort_example/tablesort_example.routing.yml
+++ b/tablesort_example/tablesort_example.routing.yml
@@ -3,4 +3,4 @@ tablesort_example_description:
   defaults:
     _controller: '\Drupal\tablesort_example\Controller\TableSortExampleController::description'
   requirements:
-    _access: 'TRUE'
+    _permission: 'access content'