diff --git a/core/lib/Drupal/Core/Plugin/Mapper/ConfigMapper.php b/core/lib/Drupal/Core/Plugin/Mapper/ConfigMapper.php
index 461236f..6c8d0b0 100644
--- a/core/lib/Drupal/Core/Plugin/Mapper/ConfigMapper.php
+++ b/core/lib/Drupal/Core/Plugin/Mapper/ConfigMapper.php
@@ -8,21 +8,27 @@
 namespace Drupal\Core\Plugin\Mapper;
 
 use Drupal\Component\Plugin\Mapper\MapperInterface;
+use Drupal\Component\Plugin\PluginManagerInterface;
 
 /**
- * @todo.
+ * Retrieves plugin instances from the configuration system.
  */
 class ConfigMapper implements MapperInterface {
 
   /**
-   * @todo.
+   * The plugin manager instance used by this mapper.
+   *
+   * @var \Drupal\Component\Plugin\PluginManagerInterface
    */
   protected $manager;
 
   /**
-   * @todo.
+   * Constructs a \Drupal\Core\Plugin\Mapper\ConfigMapper object.
+   *
+   * @param \Drupal\Component\Plugin\PluginManagerInterface $manager
+   *   The plugin manager instance to use for this mapper.
    */
-  public function __construct($manager) {
+  public function __construct(PluginManagerInterface $manager) {
     $this->manager = $manager;
   }
 
diff --git a/core/modules/aggregator/lib/Drupal/aggregator/Plugin/Derivative/CategoryBlock.php b/core/modules/aggregator/lib/Drupal/aggregator/Plugin/Derivative/CategoryBlock.php
index f881ec9..4f0cbbd 100644
--- a/core/modules/aggregator/lib/Drupal/aggregator/Plugin/Derivative/CategoryBlock.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/Plugin/Derivative/CategoryBlock.php
@@ -10,12 +10,14 @@
 use Drupal\Component\Plugin\Derivative\DerivativeInterface;
 
 /**
- * @todo.
+ * Provides block plugin definitions for aggregator categories.
  */
 class CategoryBlock implements DerivativeInterface {
 
   /**
-   * @todo.
+   * List of derivative definitions.
+   *
+   * @var array
    */
   protected $derivatives = array();
 
diff --git a/core/modules/aggregator/lib/Drupal/aggregator/Plugin/Derivative/FeedBlock.php b/core/modules/aggregator/lib/Drupal/aggregator/Plugin/Derivative/FeedBlock.php
index 575a4a8..d32bf8e 100644
--- a/core/modules/aggregator/lib/Drupal/aggregator/Plugin/Derivative/FeedBlock.php
+++ b/core/modules/aggregator/lib/Drupal/aggregator/Plugin/Derivative/FeedBlock.php
@@ -10,12 +10,14 @@
 use Drupal\Component\Plugin\Derivative\DerivativeInterface;
 
 /**
- * @todo.
+ * Provides block plugin definitions for aggregator feeds.
  */
 class FeedBlock implements DerivativeInterface {
 
   /**
-   * @todo.
+   * List of derivative definitions.
+   *
+   * @var array
    */
   protected $derivatives = array();
 
diff --git a/core/modules/block/custom_block/custom_block.admin.inc b/core/modules/block/custom_block/custom_block.admin.inc
index a45a0bf..9b8bd52 100644
--- a/core/modules/block/custom_block/custom_block.admin.inc
+++ b/core/modules/block/custom_block/custom_block.admin.inc
@@ -2,11 +2,11 @@
 
 /**
  * @file
- * @todo.
+ * Admin page callbacks for the custom block module.
  */
 
 /**
- * @todo.
+ * Form constructor for the custom blocks admin page.
  */
 function custom_block_admin_custom_block($form, &$form_state) {
   $destination = drupal_get_destination();
diff --git a/core/modules/block/custom_block/custom_block.install b/core/modules/block/custom_block/custom_block.install
index f32a6f5..4a0e4b0 100644
--- a/core/modules/block/custom_block/custom_block.install
+++ b/core/modules/block/custom_block/custom_block.install
@@ -2,7 +2,7 @@
 
 /**
  * @file
- * @todo.
+ * Install, update and uninstall functions for the custom block module.
  */
 
 /**
diff --git a/core/modules/block/custom_block/custom_block.module b/core/modules/block/custom_block/custom_block.module
index c70b285..b93b96e 100644
--- a/core/modules/block/custom_block/custom_block.module
+++ b/core/modules/block/custom_block/custom_block.module
@@ -2,7 +2,7 @@
 
 /**
  * @file
- * @todo.
+ * Allows the ability to create custom blocks through the block interface.
  */
 
 /**
diff --git a/core/modules/block/custom_block/lib/Drupal/custom_block/Plugin/Derivative/CustomBlock.php b/core/modules/block/custom_block/lib/Drupal/custom_block/Plugin/Derivative/CustomBlock.php
index 23cc00a..e3a5072 100644
--- a/core/modules/block/custom_block/lib/Drupal/custom_block/Plugin/Derivative/CustomBlock.php
+++ b/core/modules/block/custom_block/lib/Drupal/custom_block/Plugin/Derivative/CustomBlock.php
@@ -10,12 +10,14 @@
 use Drupal\Component\Plugin\Derivative\DerivativeInterface;
 
 /**
- * @todo.
+ * Provides block plugin definitions for all custom blocks.
  */
 class CustomBlock implements DerivativeInterface {
 
   /**
-   * @todo.
+   * List of derivative definitions.
+   *
+   * @var array
    */
   protected $derivatives = array();
 
diff --git a/core/modules/block/lib/Drupal/block/BlockBase.php b/core/modules/block/lib/Drupal/block/BlockBase.php
index 58017ca..0a02775 100644
--- a/core/modules/block/lib/Drupal/block/BlockBase.php
+++ b/core/modules/block/lib/Drupal/block/BlockBase.php
@@ -8,7 +8,6 @@
 namespace Drupal\block;
 
 use Drupal\Component\Plugin\PluginBase;
-use Symfony\Component\Routing\RequestContext;
 
 /**
  * An abstract block implementation to be inherited from to take care of many
@@ -17,11 +16,6 @@
 abstract class BlockBase extends PluginBase implements BlockInterface {
 
   /**
-   * @todo.
-   */
-  protected $context;
-
-  /**
    * Implements \Drupal\block\BlockInterface::settingsWrapper().
    */
   public function settingsWrapper() {
@@ -241,9 +235,9 @@ public function configureWrapper($form, &$form_state) {
       '#weight' => 0,
     );
 
-    //@TODO remove this access check and inject it in some other way.
-    // In fact this entire visibility settings section probably needs a
-    // separate user interface in the near future.
+    // @todo remove this access check and inject it in some other way. In fact
+    //   this entire visibility settings section probably needs a separate user
+    //   interface in the near future.
     $access = user_access('use PHP for settings');
     if (!empty($config['visibility']['path']['visibility']) && $config['visibility']['path']['visibility'] == BLOCK_VISIBILITY_PHP && !$access) {
       $form['visibility']['path']['visibility'] = array(
@@ -291,8 +285,8 @@ public function configureWrapper($form, &$form_state) {
       // Fetch languages.
       $languages = language_list(LANGUAGE_ALL);
       foreach ($languages as $language) {
-        // @TODO $language->name is not wrapped with t(), it should be replaced
-        // by CMI translation implementation.
+        // @todo $language->name is not wrapped with t(), it should be replaced
+        //   by CMI translation implementation.
         $langcodes_options[$language->langcode] = $language->name;
       }
       $form['visibility']['language'] = array(
diff --git a/core/modules/block/lib/Drupal/block/Plugin/Derivative/BlockPluginUI.php b/core/modules/block/lib/Drupal/block/Plugin/Derivative/BlockPluginUI.php
index da835aa..7762a7f 100644
--- a/core/modules/block/lib/Drupal/block/Plugin/Derivative/BlockPluginUI.php
+++ b/core/modules/block/lib/Drupal/block/Plugin/Derivative/BlockPluginUI.php
@@ -9,12 +9,14 @@
 use Drupal\Component\Plugin\Derivative\DerivativeInterface;
 
 /**
- * @todo.
+ * Provides block plugin definitions for each theme.
  */
 class BlockPluginUI implements DerivativeInterface {
 
   /**
-   * @todo.
+   * List of derivative definitions.
+   *
+   * @var array
    */
   protected $derivatives = array();
 
diff --git a/core/modules/block/lib/Drupal/block/Plugin/Type/BlockManager.php b/core/modules/block/lib/Drupal/block/Plugin/Type/BlockManager.php
index 39b37c7..bf89cc4 100644
--- a/core/modules/block/lib/Drupal/block/Plugin/Type/BlockManager.php
+++ b/core/modules/block/lib/Drupal/block/Plugin/Type/BlockManager.php
@@ -14,12 +14,12 @@
 use Drupal\Core\Plugin\Mapper\ConfigMapper;
 
 /**
- * @todo.
+ * Manages discovery and instantiation of block plugins.
  */
 class BlockManager extends PluginManagerBase {
 
   /**
-   * @todo.
+   * Constructs a new \Drupal\block\Plugin\Type\BlockManager object.
    */
   public function __construct() {
     $this->discovery = new AlterDecorator(new DerivativeDiscoveryDecorator(new AnnotatedClassDiscovery('block', 'block')), 'block');
diff --git a/core/modules/block/lib/Drupal/block/Plugin/system/plugin_ui/BlockPluginUI.php b/core/modules/block/lib/Drupal/block/Plugin/system/plugin_ui/BlockPluginUI.php
index 5f8c751..16358d5 100644
--- a/core/modules/block/lib/Drupal/block/Plugin/system/plugin_ui/BlockPluginUI.php
+++ b/core/modules/block/lib/Drupal/block/Plugin/system/plugin_ui/BlockPluginUI.php
@@ -20,7 +20,7 @@
  *   menu = TRUE,
  *   module = "block",
  *   all_plugins = @Translation("All Blocks"),
- *   link_title = @Translation("Configure Block"),
+ *   link_title = @Translation("Configure block"),
  *   config_path = "admin/structure/block/manage",
  *   path = "admin/structure/block/list",
  *   suffix = "add",
diff --git a/core/modules/block/tests/lib/Drupal/block_test/Plugin/block/block/TestCacheBlock.php b/core/modules/block/tests/lib/Drupal/block_test/Plugin/block/block/TestCacheBlock.php
index c07bdba..4ae387f 100644
--- a/core/modules/block/tests/lib/Drupal/block_test/Plugin/block/block/TestCacheBlock.php
+++ b/core/modules/block/tests/lib/Drupal/block_test/Plugin/block/block/TestCacheBlock.php
@@ -1,5 +1,10 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\block_test\Plugin\block\block\TestCacheBlock.
+ */
+
 namespace Drupal\block_test\Plugin\block\block;
 
 use Drupal\block\BlockBase;
@@ -7,6 +12,8 @@
 use Drupal\Core\Annotation\Translation;
 
 /**
+ * @todo.
+ *
  * @Plugin(
  *   id = "test_cache",
  *   subject = @Translation("Test block caching"),
@@ -16,7 +23,7 @@
 class TestCacheBlock extends BlockBase {
 
   /**
-   * Implements BlockInterface::settings().
+   * Overrides \Drupal\block\BlockBase::settings().
    */
   public function settings() {
     return array(
@@ -25,9 +32,12 @@ public function settings() {
   }
 
   /**
-   * Implements BlockInterface::build().
+   * Overrides \Drupal\block\BlockBase::build().
    */
   public function build() {
-    return array('#children' => variable_get('block_test_content', ''));
+    return array(
+      '#children' => variable_get('block_test_content', ''),
+    );
   }
+
 }
diff --git a/core/modules/block/tests/lib/Drupal/block_test/Plugin/block/block/TestHtmlIdBlock.php b/core/modules/block/tests/lib/Drupal/block_test/Plugin/block/block/TestHtmlIdBlock.php
index e7ca2f7..3f478d6 100644
--- a/core/modules/block/tests/lib/Drupal/block_test/Plugin/block/block/TestHtmlIdBlock.php
+++ b/core/modules/block/tests/lib/Drupal/block_test/Plugin/block/block/TestHtmlIdBlock.php
@@ -1,5 +1,10 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\block_test\Plugin\block\block\TestHtmlIdBlock.
+ */
+
 namespace Drupal\block_test\Plugin\block\block;
 
 use Drupal\block\BlockBase;
@@ -7,10 +12,13 @@
 use Drupal\Core\Annotation\Translation;
 
 /**
+ * @todo.
+ *
  * @Plugin(
  *   id = "test_html_id",
  *   subject = @Translation("Test block html id"),
  *   module = "block_test"
  * )
  */
-class TestHtmlIdBlock extends TestCacheBlock {}
+class TestHtmlIdBlock extends TestCacheBlock {
+}
diff --git a/core/modules/book/lib/Drupal/book/Plugin/block/block/BookNavigationBlock.php b/core/modules/book/lib/Drupal/book/Plugin/block/block/BookNavigationBlock.php
index 51ef9b1..36d6ac2 100644
--- a/core/modules/book/lib/Drupal/book/Plugin/block/block/BookNavigationBlock.php
+++ b/core/modules/book/lib/Drupal/book/Plugin/block/block/BookNavigationBlock.php
@@ -1,5 +1,10 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\book\Plugin\block\block\BookNavigationBlock.
+ */
+
 namespace Drupal\book\Plugin\block\block;
 
 use Drupal\block\BlockBase;
@@ -7,6 +12,8 @@
 use Drupal\Core\Annotation\Translation;
 
 /**
+ * @todo.
+ *
  * @Plugin(
  *   id = "book_navigation",
  *   subject = @Translation("Book navigation"),
@@ -16,7 +23,7 @@
 class BookNavigationBlock extends BlockBase {
 
   /**
-   * Implements BlockInterface::settings().
+   * Overrides \Drupal\block\BlockBase::settings().
    */
   public function settings() {
     return array(
@@ -26,7 +33,7 @@ public function settings() {
   }
 
   /**
-   * Implements BlockInterface::configure()
+   * Overrides \Drupal\block\BlockBase::configure()
    */
   function configure($form, &$form_state) {
     $options = array(
@@ -45,14 +52,14 @@ function configure($form, &$form_state) {
   }
 
   /**
-   * Implements BlockInterface::configureSubmit().
+   * Overrides \Drupal\block\BlockBase::configureSubmit().
    */
   public function configureSubmit($form, &$form_state) {
     $this->configuration['block_mode'] = $form_state['values']['book_block_mode'];
   }
 
   /**
-   * Implements BlockInterface::build().
+   * Overrides \Drupal\block\BlockBase::build().
    */
   public function build() {
     $current_bid = 0;
@@ -109,4 +116,5 @@ public function build() {
     }
     return array();
   }
+
 }
diff --git a/core/modules/comment/lib/Drupal/comment/Plugin/block/block/RecentBlock.php b/core/modules/comment/lib/Drupal/comment/Plugin/block/block/RecentBlock.php
index 6f151fc..8b81053 100644
--- a/core/modules/comment/lib/Drupal/comment/Plugin/block/block/RecentBlock.php
+++ b/core/modules/comment/lib/Drupal/comment/Plugin/block/block/RecentBlock.php
@@ -1,5 +1,10 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\comment\Plugin\block\block\RecentBlock.
+ */
+
 namespace Drupal\comment\Plugin\block\block;
 
 use Drupal\block\BlockBase;
@@ -7,6 +12,8 @@
 use Drupal\Core\Annotation\Translation;
 
 /**
+ * @todo.
+ *
  * @Plugin(
  *  id = "recent_comments",
  *  subject = @Translation("Recent comments"),
@@ -15,6 +22,9 @@
  */
 class RecentBlock extends BlockBase {
 
+  /**
+   * Overrides \Drupal\block\BlockBase::settings().
+   */
   public function settings() {
     return array(
       'block_count' => 10,
@@ -22,14 +32,14 @@ public function settings() {
   }
 
   /**
-   * Implements BlockInterface::access().
+   * Overrides \Drupal\block\BlockBase::access().
    */
   public function access() {
     return user_access('access comments');
   }
 
   /**
-   * Implements BlockInterface::configure().
+   * Overrides \Drupal\block\BlockBase::configure().
    */
   public function configure($form, &$form_state) {
     $form['block_count'] = array(
@@ -42,14 +52,14 @@ public function configure($form, &$form_state) {
   }
 
   /**
-   * Implements BlockInterface::configureSubmit().
+   * Overrides \Drupal\block\BlockBase::configureSubmit().
    */
   public function configureSubmit($form, &$form_state) {
     $this->configuration['block_count'] = $form_state['values']['block_count'];
   }
 
   /**
-   * Implements BlockInterface::build();
+   * Overrides \Drupal\block\BlockBase::build();
    */
   public function build() {
     return array(
@@ -57,4 +67,5 @@ public function build() {
       '#number' => $this->configuration['block_count'],
     );
   }
+
 }
diff --git a/core/modules/forum/lib/Drupal/forum/Plugin/block/block/ActiveBlock.php b/core/modules/forum/lib/Drupal/forum/Plugin/block/block/ActiveBlock.php
index 903ef1a..b74f7b3 100644
--- a/core/modules/forum/lib/Drupal/forum/Plugin/block/block/ActiveBlock.php
+++ b/core/modules/forum/lib/Drupal/forum/Plugin/block/block/ActiveBlock.php
@@ -1,61 +1,28 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\forum\Plugin\block\block\ActiveBlock.
+ */
+
 namespace Drupal\forum\Plugin\block\block;
 
-use Drupal\block\BlockBase;
 use Drupal\Core\Annotation\Plugin;
 use Drupal\Core\Annotation\Translation;
 
 /**
+ * @todo.
+ *
  * @Plugin(
  *   id = "forum_active_block",
  *   subject = @Translation("Active forum topics"),
  *   module = "forum"
  * )
  */
-class ActiveBlock extends BlockBase {
-
-  /**
-   * Implements BlockInterface::settings().
-   */
-  public function settings() {
-    return array(
-      'cache' => DRUPAL_CACHE_CUSTOM,
-      'properties' => array(
-        'administrative' => TRUE,
-      ),
-      'block_count' => 5,
-    );
-  }
-
-  /**
-   * Implements BlockInterface::access().
-   */
-  public function access() {
-    return user_access('access content');
-  }
-
-  /**
-   * Implements BlockInterface::configure().
-   */
-  public function configure($form, &$form_state) {
-    $form['block_count'] = array(
-      '#type' => 'select',
-      '#title' => t('Number of topics'),
-      '#default_value' => $this->configuration['block_count'],
-      '#options' => drupal_map_assoc(range(2, 20)));
-    return $form;
-  }
+class ActiveBlock extends ForumBlockBase {
 
   /**
-   * Implements BlockInterface::configureSubmit().
-   */
-  public function configureSubmit($form, &$form_state) {
-    $this->configuration['block_count'] = $form_state['values']['block_count'];
-  }
-
-  /**
-   * Implements BlockInterface::build().
+   * Overrides \Drupal\block\BlockBase::build().
    */
   public function build() {
     $query = db_select('forum_index', 'f')
@@ -69,4 +36,5 @@ public function build() {
       drupal_render_cache_by_query($query, 'forum_block_view'),
     );
   }
+
 }
diff --git a/core/modules/forum/lib/Drupal/forum/Plugin/block/block/ForumBlockBase.php b/core/modules/forum/lib/Drupal/forum/Plugin/block/block/ForumBlockBase.php
new file mode 100644
index 0000000..d11a9e4
--- /dev/null
+++ b/core/modules/forum/lib/Drupal/forum/Plugin/block/block/ForumBlockBase.php
@@ -0,0 +1,57 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\forum\Plugin\block\block\ForumBlockBase.
+ */
+
+namespace Drupal\forum\Plugin\block\block;
+
+use Drupal\block\BlockBase;
+
+/**
+ * Provides a base class for Forum blocks.
+ */
+abstract class ForumBlockBase extends BlockBase {
+
+  /**
+   * Overrides \Drupal\block\BlockBase::settings().
+   */
+  public function settings() {
+    return array(
+      'cache' => DRUPAL_CACHE_CUSTOM,
+      'properties' => array(
+        'administrative' => TRUE,
+      ),
+      'block_count' => 5,
+    );
+  }
+
+  /**
+   * Overrides \Drupal\block\BlockBase::access().
+   */
+  public function access() {
+    return user_access('access content');
+  }
+
+  /**
+   * Overrides \Drupal\block\BlockBase::configure().
+   */
+  public function configure($form, &$form_state) {
+    $form['block_count'] = array(
+      '#type' => 'select',
+      '#title' => t('Number of topics'),
+      '#default_value' => $this->configuration['block_count'],
+      '#options' => drupal_map_assoc(range(2, 20)),
+    );
+    return $form;
+  }
+
+  /**
+   * Overrides \Drupal\block\BlockBase::configureSubmit().
+   */
+  public function configureSubmit($form, &$form_state) {
+    $this->configuration['block_count'] = $form_state['values']['block_count'];
+  }
+
+}
diff --git a/core/modules/forum/lib/Drupal/forum/Plugin/block/block/NewBlock.php b/core/modules/forum/lib/Drupal/forum/Plugin/block/block/NewBlock.php
index 8aa0073..11e0313 100644
--- a/core/modules/forum/lib/Drupal/forum/Plugin/block/block/NewBlock.php
+++ b/core/modules/forum/lib/Drupal/forum/Plugin/block/block/NewBlock.php
@@ -1,61 +1,28 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\forum\Plugin\block\block\NewBlock.
+ */
+
 namespace Drupal\forum\Plugin\block\block;
 
-use Drupal\block\BlockBase;
 use Drupal\Core\Annotation\Plugin;
 use Drupal\Core\Annotation\Translation;
 
 /**
+ * @todo.
+ *
  * @Plugin(
  *   id = "forum_new_block",
  *   subject = @Translation("New forum topics"),
  *   module = "forum"
  * )
  */
-class NewBlock extends BlockBase {
-
-  /**
-   * Implements BlockInterface::settings().
-   */
-  public function settings() {
-    return array(
-      'cache' => DRUPAL_CACHE_CUSTOM,
-      'properties' => array(
-        'administrative' => TRUE,
-      ),
-      'block_count' => 5,
-    );
-  }
-
-  /**
-   * Implements BlockInterface::access().
-   */
-  public function access() {
-    return user_access('access content');
-  }
-
-  /**
-   * Implements BlockInterface::configure().
-   */
-  public function configure($form, &$form_state) {
-    $form['block_count'] = array(
-      '#type' => 'select',
-      '#title' => t('Number of topics'),
-      '#default_value' => $this->configuration['block_count'],
-      '#options' => drupal_map_assoc(range(2, 20)));
-    return $form;
-  }
+class NewBlock extends ForumBlockBase {
 
   /**
-   * Implements BlockInterface::configureSubmit().
-   */
-  public function configureSubmit($form, &$form_state) {
-    $this->configuration['block_count'] = $form_state['values']['block_count'];
-  }
-
-  /**
-   * Implements BlockInterface::build().
+   * Overrides \Drupal\block\BlockBase::build().
    */
   public function build() {
     $query = db_select('forum_index', 'f')
@@ -69,4 +36,5 @@ public function build() {
       drupal_render_cache_by_query($query, 'forum_block_view'),
     );
   }
+
 }
diff --git a/core/modules/language/lib/Drupal/language/Plugin/Derivative/LanguageBlock.php b/core/modules/language/lib/Drupal/language/Plugin/Derivative/LanguageBlock.php
index 0dff21a..827b9b5 100644
--- a/core/modules/language/lib/Drupal/language/Plugin/Derivative/LanguageBlock.php
+++ b/core/modules/language/lib/Drupal/language/Plugin/Derivative/LanguageBlock.php
@@ -1,14 +1,28 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\language\Plugin\Derivative\LanguageBlock.
+ */
+
 namespace Drupal\language\Plugin\Derivative;
 
 use Drupal\Component\Plugin\Derivative\DerivativeInterface;
 
+/**
+ * Provides language switcher block plugin definitions for all languages.
+ */
 class LanguageBlock implements DerivativeInterface {
+
+  /**
+   * List of derivative definitions.
+   *
+   * @var array
+   */
   protected $derivatives = array();
 
   /**
-   * Implements DerivativeInterface::getDerivativeDefinition().
+   * Implements \Drupal\Component\Plugin\Derivative\DerivativeInterface::getDerivativeDefinition().
    */
   public function getDerivativeDefinition($derivative_id, array $base_plugin_definition) {
     if (!empty($this->derivatives) && !empty($this->derivatives[$derivative_id])) {
@@ -19,7 +33,7 @@ public function getDerivativeDefinition($derivative_id, array $base_plugin_defin
   }
 
   /**
-   * Implements DerivativeInterface::getDerivativeDefinitions().
+   * Implements \Drupal\Component\Plugin\Derivative\DerivativeInterface::getDerivativeDefinitions().
    */
   public function getDerivativeDefinitions(array $base_plugin_definition) {
     include_once DRUPAL_ROOT . '/core/includes/language.inc';
@@ -31,4 +45,5 @@ public function getDerivativeDefinitions(array $base_plugin_definition) {
     }
     return $this->derivatives;
   }
+
 }
diff --git a/core/modules/language/lib/Drupal/language/Plugin/block/block/LanguageBlock.php b/core/modules/language/lib/Drupal/language/Plugin/block/block/LanguageBlock.php
index a4d689c..1714748 100644
--- a/core/modules/language/lib/Drupal/language/Plugin/block/block/LanguageBlock.php
+++ b/core/modules/language/lib/Drupal/language/Plugin/block/block/LanguageBlock.php
@@ -1,5 +1,10 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\language\Plugin\block\block\LanguageBlock.
+ */
+
 namespace Drupal\language\Plugin\block\block;
 
 use Drupal\block\BlockBase;
@@ -7,6 +12,8 @@
 use Drupal\Core\Annotation\Translation;
 
 /**
+ * @todo.
+ *
  * @Plugin(
  *   id = "language_block",
  *   subject = @Translation("Language switcher"),
@@ -17,14 +24,14 @@
 class LanguageBlock extends BlockBase {
 
   /**
-   * Implements BlockInterface::access().
+   * Overrides \Drupal\block\BlockBase::access().
    */
   function access() {
     return language_multilingual();
   }
 
   /**
-   * Implements BlockInterface::build().
+   * Overrides \Drupal\block\BlockBase::build().
    */
   function build() {
     $path = drupal_is_front_page() ? '<front>' : current_path();
@@ -32,11 +39,16 @@ function build() {
     $links = language_negotiation_get_switch_links($type, $path);
 
     if (isset($links->links)) {
-      $class = "language-switcher-{$links->method_id}";
-      $variables = array('links' => $links->links, 'attributes' => array('class' => array($class)));
       return array(
-        '#children' => theme('links__language_block', $variables)
+        '#theme' => 'links__language_block',
+        '#links' => $links->links,
+        '#attributes' => array(
+          'class' => array(
+            "language-switcher-{$links->method_id}",
+          ),
+        ),
       );
     }
   }
+
 }
diff --git a/core/modules/menu/lib/Drupal/menu/Plugin/Derivative/MenuBlock.php b/core/modules/menu/lib/Drupal/menu/Plugin/Derivative/MenuBlock.php
index 3285cbd..caa6931 100644
--- a/core/modules/menu/lib/Drupal/menu/Plugin/Derivative/MenuBlock.php
+++ b/core/modules/menu/lib/Drupal/menu/Plugin/Derivative/MenuBlock.php
@@ -10,12 +10,12 @@
 use Drupal\system\Plugin\Derivative\SystemMenuBlock;
 
 /**
- * @todo.
+ * Provides block plugin definitions for custom menus.
  */
 class MenuBlock extends SystemMenuBlock {
 
   /**
-   * Implements DerivativeInterface::getDerivativeDefinitions().
+   * Implements \Drupal\Component\Plugin\Derivative\DerivativeInterface::getDerivativeDefinitions().
    */
   public function getDerivativeDefinitions(array $base_plugin_definition) {
     foreach (menu_get_menus(FALSE) as $menu => $name) {
diff --git a/core/modules/menu/lib/Drupal/menu/Plugin/block/block/MenuBlock.php b/core/modules/menu/lib/Drupal/menu/Plugin/block/block/MenuBlock.php
index c357958..5e16f14 100644
--- a/core/modules/menu/lib/Drupal/menu/Plugin/block/block/MenuBlock.php
+++ b/core/modules/menu/lib/Drupal/menu/Plugin/block/block/MenuBlock.php
@@ -1,5 +1,10 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\menu\Plugin\block\block\MenuBlock.
+ */
+
 namespace Drupal\menu\Plugin\block\block;
 
 use Drupal\system\Plugin\block\block\SystemMenuBlock;
@@ -7,6 +12,8 @@
 use Drupal\Core\Annotation\Translation;
 
 /**
+ * @todo.
+ *
  * @Plugin(
  *   id = "menu_menu_block",
  *   subject = @Translation("Menu"),
diff --git a/core/modules/node/lib/Drupal/node/Plugin/block/block/RecentBlock.php b/core/modules/node/lib/Drupal/node/Plugin/block/block/RecentBlock.php
index de31e7b..fb86c80 100644
--- a/core/modules/node/lib/Drupal/node/Plugin/block/block/RecentBlock.php
+++ b/core/modules/node/lib/Drupal/node/Plugin/block/block/RecentBlock.php
@@ -1,5 +1,10 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\node\Plugin\block\block\RecentBlock.
+ */
+
 namespace Drupal\node\Plugin\block\block;
 
 use Drupal\block\BlockBase;
@@ -7,6 +12,8 @@
 use Drupal\Core\Annotation\Translation;
 
 /**
+ * @todo.
+ *
  * @Plugin(
  *   id = "node_recent_block",
  *   subject = @Translation("Recent content"),
@@ -16,7 +23,7 @@
 class RecentBlock extends BlockBase {
 
   /**
-   * Implements BlockInterface::settings().
+   * Overrides \Drupal\block\BlockBase::settings().
    */
   public function settings() {
     return array(
@@ -25,14 +32,14 @@ public function settings() {
   }
 
   /**
-   * Implements BlockInterface::access().
+   * Overrides \Drupal\block\BlockBase::access().
    */
   public function access() {
     return user_access('access content');
   }
 
   /**
-   * Implements BlockInterface::configure().
+   * Overrides \Drupal\block\BlockBase::configure().
    */
   public function configure($form, &$form_state) {
     $form['block_count'] = array(
@@ -45,14 +52,14 @@ public function configure($form, &$form_state) {
   }
 
   /**
-   * Implements BlockInterface::configureSubmit().
+   * Overrides \Drupal\block\BlockBase::configureSubmit().
    */
   public function configureSubmit($form, &$form_state) {
     $this->configuration['block_count'] = $form_state['values']['block_count'];
   }
 
   /**
-   * Implements BlockInterface::build();
+   * Overrides \Drupal\block\BlockBase::build();
    */
   public function build() {
     if ($nodes = node_get_recent($this->configuration['block_count'])) {
@@ -67,4 +74,5 @@ public function build() {
       );
     }
   }
+
 }
diff --git a/core/modules/node/lib/Drupal/node/Plugin/block/block/SyndicateBlock.php b/core/modules/node/lib/Drupal/node/Plugin/block/block/SyndicateBlock.php
index 524b945..e7c962c 100644
--- a/core/modules/node/lib/Drupal/node/Plugin/block/block/SyndicateBlock.php
+++ b/core/modules/node/lib/Drupal/node/Plugin/block/block/SyndicateBlock.php
@@ -1,5 +1,10 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\node\Plugin\block\block\SyndicateBlock.
+ */
+
 namespace Drupal\node\Plugin\block\block;
 
 use Drupal\block\BlockBase;
@@ -7,6 +12,8 @@
 use Drupal\Core\Annotation\Translation;
 
 /**
+ * @todo.
+ *
  * @Plugin(
  *   id = "node_syndicate_block",
  *   subject = @Translation("Syndicate"),
@@ -16,7 +23,7 @@
 class SyndicateBlock extends BlockBase {
 
   /**
-   * Implements BlockInterface::settings().
+   * Overrides \Drupal\block\BlockBase::settings().
    */
   public function settings() {
     return array(
@@ -25,14 +32,14 @@ public function settings() {
   }
 
   /**
-   * Implements BlockInterface::access().
+   * Overrides \Drupal\block\BlockBase::access().
    */
   public function access() {
     return user_access('access content');
   }
 
   /**
-   * Implements BlockInterface::build();
+   * Overrides \Drupal\block\BlockBase::build();
    */
   public function build() {
     return array(
@@ -40,4 +47,5 @@ public function build() {
       '#url' => 'rss.xml',
     );
   }
+
 }
diff --git a/core/modules/poll/lib/Drupal/poll/Plugin/block/block/PollRecentBlock.php b/core/modules/poll/lib/Drupal/poll/Plugin/block/block/PollRecentBlock.php
index 81ec76f..4db6d8a 100644
--- a/core/modules/poll/lib/Drupal/poll/Plugin/block/block/PollRecentBlock.php
+++ b/core/modules/poll/lib/Drupal/poll/Plugin/block/block/PollRecentBlock.php
@@ -1,5 +1,10 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\poll\Plugin\block\block\PollRecentBlock.
+ */
+
 namespace Drupal\poll\Plugin\block\block;
 
 use Drupal\block\BlockBase;
@@ -7,6 +12,8 @@
 use Drupal\Core\Annotation\Translation;
 
 /**
+ * @todo.
+ *
  * @Plugin(
  *   id = "poll_recent_block",
  *   subject = @Translation("Most recent poll"),
@@ -14,10 +21,16 @@
  * )
  */
 class PollRecentBlock extends BlockBase {
+
+  /**
+   * Stores the node ID of the latest poll.
+   *
+   * @var int
+   */
   protected $record;
 
   /**
-   * Implements BlockInterface::settings().
+   * Overrides \Drupal\block\BlockBase::settings().
    */
   public function settings() {
     return array(
@@ -28,7 +41,7 @@ public function settings() {
   }
 
   /**
-   * Implements BlockInterface::access().
+   * Overrides \Drupal\block\BlockBase::access().
    */
   public function access() {
     if (user_access('access content')) {
@@ -44,7 +57,7 @@ public function access() {
 
       $record = $select->execute()->fetchObject();
       if ($record) {
-        $this->record = $record;
+        $this->record = $record->nid;
         return TRUE;
       }
     }
@@ -52,10 +65,10 @@ public function access() {
   }
 
   /**
-   * Implements BlockInterface::build().
+   * Overrides \Drupal\block\BlockBase::build().
    */
   public function build() {
-    $poll = node_load($this->record->nid);
+    $poll = node_load($this->record);
     if ($poll->nid) {
       $poll = poll_block_latest_poll_view($poll);
       return array(
@@ -64,4 +77,5 @@ public function build() {
     }
     return array();
   }
-}
\ No newline at end of file
+
+}
diff --git a/core/modules/search/lib/Drupal/search/Plugin/block/block/SearchBlock.php b/core/modules/search/lib/Drupal/search/Plugin/block/block/SearchBlock.php
index 008daa2..94cd343 100644
--- a/core/modules/search/lib/Drupal/search/Plugin/block/block/SearchBlock.php
+++ b/core/modules/search/lib/Drupal/search/Plugin/block/block/SearchBlock.php
@@ -1,5 +1,10 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\search\Plugin\block\block\SearchBlock.
+ */
+
 namespace Drupal\search\Plugin\block\block;
 
 use Drupal\block\BlockBase;
@@ -7,6 +12,8 @@
 use Drupal\Core\Annotation\Translation;
 
 /**
+ * @todo.
+ *
  * @Plugin(
  *   id = "search_form_block",
  *   subject = @Translation("Search form"),
@@ -16,16 +23,17 @@
 class SearchBlock extends BlockBase {
 
   /**
-   * Implements BlockInterface::access().
+   * Overrides \Drupal\block\BlockBase::access().
    */
   public function access() {
     return user_access('search content');
   }
 
   /**
-   * Implements BlockInterface::build().
+   * Overrides \Drupal\block\BlockBase::build().
    */
   public function build() {
     return array(drupal_get_form('search_block_form'));
   }
+
 }
diff --git a/core/modules/shortcut/lib/Drupal/shortcut/Plugin/block/block/ShortcutsBlock.php b/core/modules/shortcut/lib/Drupal/shortcut/Plugin/block/block/ShortcutsBlock.php
index da184df..fe17ca1 100644
--- a/core/modules/shortcut/lib/Drupal/shortcut/Plugin/block/block/ShortcutsBlock.php
+++ b/core/modules/shortcut/lib/Drupal/shortcut/Plugin/block/block/ShortcutsBlock.php
@@ -1,5 +1,10 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\shortcut\Plugin\block\block\ShortcutsBlock.
+ */
+
 namespace Drupal\shortcut\Plugin\block\block;
 
 use Drupal\block\BlockBase;
@@ -7,6 +12,8 @@
 use Drupal\Core\Annotation\Translation;
 
 /**
+ * @todo.
+ *
  * @Plugin(
  *  id = "shortcuts",
  *  subject = @Translation("Shortcuts"),
@@ -16,12 +23,12 @@
 class ShortcutsBlock extends BlockBase {
 
   /**
-   * Implements BlockInterface::build().
+   * Overrides \Drupal\block\BlockBase::build().
    */
   public function build() {
-    $shortcut_set = shortcut_current_displayed_set();
     return array(
-      shortcut_renderable_links($shortcut_set),
+      shortcut_renderable_links(shortcut_current_displayed_set()),
     );
   }
+
 }
diff --git a/core/modules/statistics/lib/Drupal/statistics/Plugin/block/block/StatisticsPopularBlock.php b/core/modules/statistics/lib/Drupal/statistics/Plugin/block/block/StatisticsPopularBlock.php
index ba09d08..6465a2a 100644
--- a/core/modules/statistics/lib/Drupal/statistics/Plugin/block/block/StatisticsPopularBlock.php
+++ b/core/modules/statistics/lib/Drupal/statistics/Plugin/block/block/StatisticsPopularBlock.php
@@ -1,5 +1,10 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\statistics\Plugin\block\block\StatisticsPopularBlock.
+ */
+
 namespace Drupal\statistics\Plugin\block\block;
 
 use Drupal\block\BlockBase;
@@ -7,6 +12,8 @@
 use Drupal\Core\Annotation\Translation;
 
 /**
+ * Provides a 'Popular content' block.
+ *
  * @Plugin(
  *   id = "statistics_popular_block",
  *   subject = @Translation("Popular content"),
@@ -14,12 +21,30 @@
  * )
  */
 class StatisticsPopularBlock extends BlockBase {
+
+  /**
+   * Number of day's top views to display.
+   *
+   * @var int
+   */
   protected $day_list;
+
+  /**
+   * Number of all time views to display.
+   *
+   * @var int
+   */
   protected $all_time_list;
+
+  /**
+   * Number of most recent views to display.
+   *
+   * @var int
+   */
   protected $last_list;
 
   /**
-   * Implements BlockInterface::settings().
+   * Overrides \Drupal\block\BlockBase::settings().
    */
   public function settings() {
     return array(
@@ -30,7 +55,7 @@ public function settings() {
   }
 
     /**
-   * Implements BlockInterface::access().
+   * Overrides \Drupal\block\BlockBase::access().
    */
   public function access() {
     if (user_access('access content')) {
@@ -52,37 +77,37 @@ public function access() {
   }
 
   /**
-   * Implements BlockInterface::configure().
+   * Overrides \Drupal\block\BlockBase::configure().
    */
   public function configure($form, &$form_state) {
-    // Popular content block settings
+    // Popular content block settings.
     $numbers = array('0' => t('Disabled')) + drupal_map_assoc(array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 40));
     $form['statistics_block_top_day_num'] = array(
      '#type' => 'select',
      '#title' => t("Number of day's top views to display"),
      '#default_value' => $this->configuration['top_day_num'],
      '#options' => $numbers,
-     '#description' => t('How many content items to display in "day" list.')
+     '#description' => t('How many content items to display in "day" list.'),
     );
     $form['statistics_block_top_all_num'] = array(
       '#type' => 'select',
       '#title' => t('Number of all time views to display'),
       '#default_value' => $this->configuration['top_all_num'],
       '#options' => $numbers,
-      '#description' => t('How many content items to display in "all time" list.')
+      '#description' => t('How many content items to display in "all time" list.'),
     );
     $form['statistics_block_top_last_num'] = array(
       '#type' => 'select',
       '#title' => t('Number of most recent views to display'),
       '#default_value' => $this->configuration['top_last_num'],
       '#options' => $numbers,
-      '#description' => t('How many content items to display in "recently viewed" list.')
+      '#description' => t('How many content items to display in "recently viewed" list.'),
     );
     return $form;
   }
 
   /**
-   * Implements BlockInterface::configureSubmit().
+   * Overrides \Drupal\block\BlockBase::configureSubmit().
    */
   public function configureSubmit($form, &$form_state) {
     $this->configuration['top_day_num'] = $form_state['values']['statistics_block_top_day_num'];
@@ -91,7 +116,7 @@ public function configureSubmit($form, &$form_state) {
   }
 
   /**
-   * Implements BlockInterface::build().
+   * Overrides \Drupal\block\BlockBase::build().
    */
   public function build() {
     $content = array();
diff --git a/core/modules/system/lib/Drupal/system/Plugin/Derivative/SystemMenuBlock.php b/core/modules/system/lib/Drupal/system/Plugin/Derivative/SystemMenuBlock.php
index 9ab2455..bb2f0d7 100644
--- a/core/modules/system/lib/Drupal/system/Plugin/Derivative/SystemMenuBlock.php
+++ b/core/modules/system/lib/Drupal/system/Plugin/Derivative/SystemMenuBlock.php
@@ -1,14 +1,28 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\system\Plugin\Derivative\SystemMenuBlock.
+ */
+
 namespace Drupal\system\Plugin\Derivative;
 
 use Drupal\Component\Plugin\Derivative\DerivativeInterface;
 
+/**
+ * Provides block plugin definitions for system menus.
+ */
 class SystemMenuBlock implements DerivativeInterface {
+
+  /**
+   * List of derivative definitions.
+   *
+   * @var array
+   */
   protected $derivatives = array();
 
   /**
-   * Implements DerivativeInterface::getDerivativeDefinition().
+   * Implements \Drupal\Component\Plugin\Derivative\DerivativeInterface::getDerivativeDefinition().
    */
   public function getDerivativeDefinition($derivative_id, array $base_plugin_definition) {
     if (!empty($this->derivatives) && !empty($this->derivatives[$derivative_id])) {
@@ -19,7 +33,7 @@ public function getDerivativeDefinition($derivative_id, array $base_plugin_defin
   }
 
   /**
-   * Implements DerivativeInterface::getDerivativeDefinitions().
+   * Implements \Drupal\Component\Plugin\Derivative\DerivativeInterface::getDerivativeDefinitions().
    */
   public function getDerivativeDefinitions(array $base_plugin_definition) {
     foreach (menu_list_system_menus() as $menu => $name) {
diff --git a/core/modules/system/lib/Drupal/system/Plugin/PluginUIBase.php b/core/modules/system/lib/Drupal/system/Plugin/PluginUIBase.php
index fce8288..ce84dec 100644
--- a/core/modules/system/lib/Drupal/system/Plugin/PluginUIBase.php
+++ b/core/modules/system/lib/Drupal/system/Plugin/PluginUIBase.php
@@ -1,10 +1,22 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\system\Plugin\PluginUIBase.
+ */
+
 namespace Drupal\system\Plugin;
 
 use Drupal\Component\Plugin\PluginBase;
 
-abstract class PluginUIBase extends PluginBase {
+/**
+ * @todo.
+ */
+abstract class PluginUIBase extends PluginBase implements PluginUIInterface {
+
+  /**
+   * @todo.
+   */
   public function form($form, &$form_state, $plugin, $facet) {
     $plugin_definition = $this->getDefinition();
     $manager = new $plugin_definition['manager']();
@@ -51,35 +63,64 @@ public function form($form, &$form_state, $plugin, $facet) {
     return $form;
   }
 
-  public function formValidate($form, &$form_state) {}
+  /**
+   * @todo.
+   */
+  public function formValidate($form, &$form_state) {
+  }
 
-  public function formSubmit($form, &$form_state) {}
+  /**
+   * @todo.
+   */
+  public function formSubmit($form, &$form_state) {
+  }
 
+  /**
+   * @todo.
+   */
   public function excludeDefinitions($definitions) {
     return $definitions;
   }
 
+  /**
+   * @todo.
+   */
   public function access($plugin_id) {
     $definition = $this->getDefinition($plugin_id);
     return call_user_func_array('user_access', $definition['access_arguments']);
   }
 
+  /**
+   * @todo.
+   */
   public function row($plugin, $plugin_definition, $plugin_id, $config) {
     return array($config['title'], l($plugin_definition['link_title'], $plugin_definition['config_path'] . '/' . $plugin_id));
   }
 
+  /**
+   * @todo.
+   */
   public function facetLink($facet, $plugin, $plugin_definition, $plugin_id, $config, $key) {
     return array('title' => $config[$key], 'href' => $plugin_definition['path'] . '/' . $plugin . '/' . $facet . ':' . $config[$key]);
   }
 
+  /**
+   * @todo.
+   */
   public function allPluginsUrl($plugin, $plugin_definition, $plugin_id, $config) {
     return $plugin_definition['path'] . '/' . $plugin . '/add';
   }
 
+  /**
+   * @todo.
+   */
   public function tableHeader() {
     return array(t('Title'), t('Operations'));
   }
 
+  /**
+   * @todo.
+   */
   public function facetCompare($facet, $config) {
     list($facet_type, $option) = explode(':', $facet);
     return $option == $config[$facet_type];
diff --git a/core/modules/system/lib/Drupal/system/Plugin/PluginUIInterface.php b/core/modules/system/lib/Drupal/system/Plugin/PluginUIInterface.php
index e05e90f..f90388c 100644
--- a/core/modules/system/lib/Drupal/system/Plugin/PluginUIInterface.php
+++ b/core/modules/system/lib/Drupal/system/Plugin/PluginUIInterface.php
@@ -1,16 +1,32 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\system\Plugin\PluginUIInterface.
+ */
+
 namespace Drupal\system\Plugin;
 
 /**
- * Interface definition for PluginUI plugins.
+ * Interface definition for Plugin UI plugins.
  */
 interface PluginUIInterface {
 
   /**
    * Create a form array.
    *
-   * @return array().
+   * @param array $form
+   *   An associative array containing the structure of the form.
+   * @param array $form_state
+   *   An associative array containing the current state of the form.
+   * @param string $plugin
+   *   @todo.
+   * @param string|null $facet
+   *   @todo.
+   *
+   * @return array
+   *   Returns the form structure as an array.
    */
   public function form($form, &$form_state, $plugin, $facet);
+
 }
diff --git a/core/modules/system/lib/Drupal/system/Plugin/Type/PluginUIManager.php b/core/modules/system/lib/Drupal/system/Plugin/Type/PluginUIManager.php
index 4eff8d7..64a877c 100644
--- a/core/modules/system/lib/Drupal/system/Plugin/Type/PluginUIManager.php
+++ b/core/modules/system/lib/Drupal/system/Plugin/Type/PluginUIManager.php
@@ -1,5 +1,10 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\system\Plugin\Type\PluginUIManager.
+ */
+
 namespace Drupal\system\Plugin\Type;
 
 use Drupal\Component\Plugin\PluginManagerBase;
@@ -7,12 +12,22 @@
 use Drupal\Core\Plugin\Discovery\AnnotatedClassDiscovery;
 use Drupal\Component\Plugin\Factory\ReflectionFactory;
 
+/**
+ * Manages discovery and instantiation of Plugin UI plugins.
+ */
 class PluginUIManager extends PluginManagerBase {
+
+  /**
+   * Constructs a \Drupal\system\Plugin\Type\PluginUIManager object.
+   */
   public function __construct() {
     $this->discovery = new DerivativeDiscoveryDecorator(new AnnotatedClassDiscovery('system', 'plugin_ui'));
     $this->factory = new ReflectionFactory($this);
   }
 
+  /**
+   * Overrides \Drupal\Component\Plugin\PluginManagerBase::processDefinition().
+   */
   protected function processDefinition(&$definition, $plugin_id) {
     $definition += array(
       'default_task' => TRUE,
@@ -20,4 +35,5 @@ protected function processDefinition(&$definition, $plugin_id) {
       'task_suffix' => 'view',
     );
   }
-}
\ No newline at end of file
+
+}
diff --git a/core/modules/system/lib/Drupal/system/Plugin/block/block/SystemHelpBlock.php b/core/modules/system/lib/Drupal/system/Plugin/block/block/SystemHelpBlock.php
index 7bfb5e2..0239e0a 100644
--- a/core/modules/system/lib/Drupal/system/Plugin/block/block/SystemHelpBlock.php
+++ b/core/modules/system/lib/Drupal/system/Plugin/block/block/SystemHelpBlock.php
@@ -1,5 +1,10 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\system\Plugin\block\block\SystemHelpBlock.
+ */
+
 namespace Drupal\system\Plugin\block\block;
 
 use Drupal\block\BlockBase;
@@ -7,6 +12,8 @@
 use Drupal\Core\Annotation\Translation;
 
 /**
+ * @todo.
+ *
  * @Plugin(
  *   id = "system_help_block",
  *   subject = @Translation("System Help"),
@@ -14,25 +21,29 @@
  * )
  */
 class SystemHelpBlock extends BlockBase {
-  private $help;
 
   /**
-   * Implements BlockInterface::access().
+   * Stores the help text associated with the active menu item.
+   *
+   * @var string
+   */
+  protected $help;
+
+  /**
+   * Overrides \Drupal\block\BlockBase::access().
    */
   public function access() {
     $this->help = menu_get_active_help();
-    return $this->help ? TRUE : FALSE;
+    return (bool) $this->help;
   }
 
   /**
-   * Implements BlockInterface::build().
+   * Overrides \Drupal\block\BlockBase::build().
    */
   public function build() {
-    if (empty($this->help)) {
-      $this->help = menu_get_active_help();
-    }
     return array(
       '#children' => $this->help,
     );
   }
+
 }
diff --git a/core/modules/system/lib/Drupal/system/Plugin/block/block/SystemMainBlock.php b/core/modules/system/lib/Drupal/system/Plugin/block/block/SystemMainBlock.php
index 2fe6ce4..41d6487 100644
--- a/core/modules/system/lib/Drupal/system/Plugin/block/block/SystemMainBlock.php
+++ b/core/modules/system/lib/Drupal/system/Plugin/block/block/SystemMainBlock.php
@@ -1,5 +1,10 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\system\Plugin\block\block\SystemMainBlock.
+ */
+
 namespace Drupal\system\Plugin\block\block;
 
 use Drupal\block\BlockBase;
@@ -7,6 +12,8 @@
 use Drupal\Core\Annotation\Translation;
 
 /**
+ * @todo.
+ *
  * @Plugin(
  *   id = "system_main_block",
  *   subject = @Translation("Main page content"),
@@ -16,11 +23,12 @@
 class SystemMainBlock extends BlockBase {
 
   /**
-   * Implements BlockInterface::build().
+   * Overrides \Drupal\block\BlockBase::build().
    */
   public function build() {
     return array(
       drupal_set_page_content()
     );
   }
+
 }
diff --git a/core/modules/system/lib/Drupal/system/Plugin/block/block/SystemMenuBlock.php b/core/modules/system/lib/Drupal/system/Plugin/block/block/SystemMenuBlock.php
index f570fa0..1bb5989 100644
--- a/core/modules/system/lib/Drupal/system/Plugin/block/block/SystemMenuBlock.php
+++ b/core/modules/system/lib/Drupal/system/Plugin/block/block/SystemMenuBlock.php
@@ -1,5 +1,10 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\system\Plugin\block\block\SystemMenuBlock.
+ */
+
 namespace Drupal\system\Plugin\block\block;
 
 use Drupal\block\BlockBase;
@@ -7,6 +12,8 @@
 use Drupal\Core\Annotation\Translation;
 
 /**
+ * @todo.
+ *
  * @Plugin(
  *   id = "system_menu_block",
  *   subject = @Translation("System Menu"),
@@ -17,7 +24,7 @@
 class SystemMenuBlock extends BlockBase {
 
   /**
-   * Implements BlockInterface::access().
+   * Overrides \Drupal\block\BlockBase::access().
    */
   public function access() {
     // @todo The 'Tools' menu should be available to anonymous users.
@@ -26,7 +33,7 @@ public function access() {
   }
 
   /**
-   * Implements BlockInterface::build().
+   * Overrides \Drupal\block\BlockBase::build().
    */
   public function build() {
     list($plugin, $derivative) = explode(':', $this->getPluginId());
@@ -34,4 +41,5 @@ public function build() {
     $menu = substr($derivative, 5);
     return menu_tree($menu);
   }
+
 }
diff --git a/core/modules/system/lib/Drupal/system/Plugin/block/block/SystemPoweredByBlock.php b/core/modules/system/lib/Drupal/system/Plugin/block/block/SystemPoweredByBlock.php
index 5c6e0b9..7faceea 100644
--- a/core/modules/system/lib/Drupal/system/Plugin/block/block/SystemPoweredByBlock.php
+++ b/core/modules/system/lib/Drupal/system/Plugin/block/block/SystemPoweredByBlock.php
@@ -1,5 +1,10 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\system\Plugin\block\block\SystemPoweredByBlock.
+ */
+
 namespace Drupal\system\Plugin\block\block;
 
 use Drupal\block\BlockBase;
@@ -7,6 +12,8 @@
 use Drupal\Core\Annotation\Translation;
 
 /**
+ * @todo.
+ *
  * @Plugin(
  *   id = "system_powered_by_block",
  *   subject = @Translation("Powered by Drupal"),
@@ -16,11 +23,12 @@
 class SystemPoweredByBlock extends BlockBase {
 
   /**
-   * Implements BlockInterface::build().
+   * Overrides \Drupal\block\BlockBase::build().
    */
   public function build() {
     return array(
       '#children' => theme('system_powered_by'),
     );
   }
+
 }
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 049238e..6cc5b9d 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -1124,41 +1124,27 @@ function system_menu() {
 }
 
 /**
- * A simple wrapper function for proxying to the plugin class' form method.
+ * Proxies to the plugin class' form method.
  */
 function system_plugin_ui_form($form, &$form_state, $plugin, $facet = NULL) {
-  $ui = drupal_container()->get('plugin.manager.system.plugin_ui')->createInstance($plugin);
-  $form = $ui->form($form, $form_state, $plugin, $facet);
+  $plugin_ui = drupal_container()->get('plugin.manager.system.plugin_ui')->createInstance($plugin);
+  $form = $plugin_ui->form($form, $form_state, $plugin, $facet);
+  $form['#validate'][] = array($plugin_ui, 'formValidate');
+  $form['#submit'][] = array($plugin_ui, 'formSubmit');
   return $form;
 }
 
 /**
- * A simple wrapper function for proxying to the plugin class' validate method.
- */
-function system_plugin_ui_form_validate($form, &$form_state) {
-  $form_state['values']['instance']->formValidate($form, $form_state);
-}
-
-/**
- * A simple wrapper function for proxying to the plugin class' submit method.
- */
-function system_plugin_ui_form_submit($form, &$form_state) {
-  $form_state['values']['instance']->formSubmit($form, $form_state);
-}
-
-/**
- * A generic autocomplete page callback for any plugin system tied to a plugin
- * ui plugin.
+ * Page callback: Autocomplete any plugin system tied to a plugin UI plugin.
  */
 function system_plugin_autocomplete($plugin_id, $string = '') {
   $matches = array();
-  $ui = drupal_container()->get('plugin.manager.system.plugin_ui')->getDefinition($plugin_id);
-  $manager = new $ui['manager']();
   if ($string) {
-    $plugins = $manager->getDefinitions();
+    $plugin_ui = drupal_container()->get('plugin.manager.system.plugin_ui')->getDefinition($plugin_id);
+    $manager = new $plugin_ui['manager']();
     $titles = array();
-    foreach($plugins as $plugin_id => $plugin) {
-      $titles[$plugin_id] = $plugin[$ui['title_attribute']];
+    foreach($manager->getDefinitions() as $plugin_id => $plugin) {
+      $titles[$plugin_id] = $plugin[$plugin_ui['title_attribute']];
     }
     $matches = preg_grep("/\b". $string . "/i", $titles);
   }
@@ -1170,8 +1156,8 @@ function system_plugin_autocomplete($plugin_id, $string = '') {
  * A simple wrapper function for proxying to the plugin class' access method.
  */
 function system_plugin_ui_access($plugin, $facet = NULL) {
-  $ui = drupal_container()->get('plugin.manager.system.plugin_ui')->createInstance($plugin);
-  return $ui->access($plugin, $facet);
+  $plugin_ui = drupal_container()->get('plugin.manager.system.plugin_ui')->createInstance($plugin);
+  return $plugin_ui->access($plugin, $facet);
 }
 
 /**
@@ -2655,13 +2641,10 @@ function system_preprocess_block(&$variables) {
 }
 
 /**
- * Processes variables for block-admin-display-form.tpl.php.
+ * Implements hook_preprocess_HOOK() for system-plugin-ui-form.tpl.php.
  *
  * The $variables array contains the following arguments:
  * - $form
- *
- * @see block-admin-display.tpl.php
- * @see theme_block_admin_display()
  */
 function template_preprocess_system_plugin_ui_form(&$variables) {
   drupal_add_css(drupal_get_path('module', 'system') . '/system.plugin.ui.css');
diff --git a/core/modules/user/lib/Drupal/user/Plugin/block/block/UserLoginBlock.php b/core/modules/user/lib/Drupal/user/Plugin/block/block/UserLoginBlock.php
index d363ad1..42de0ad 100644
--- a/core/modules/user/lib/Drupal/user/Plugin/block/block/UserLoginBlock.php
+++ b/core/modules/user/lib/Drupal/user/Plugin/block/block/UserLoginBlock.php
@@ -1,5 +1,10 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\user\Plugin\block\block\UserLoginBlock.
+ */
+
 namespace Drupal\user\Plugin\block\block;
 
 use Drupal\block\BlockBase;
@@ -7,6 +12,8 @@
 use Drupal\Core\Annotation\Translation;
 
 /**
+ * @todo.
+ *
  * @Plugin(
  *   id = "user_login_block",
  *   subject = @Translation("User login"),
@@ -16,15 +23,14 @@
 class UserLoginBlock extends BlockBase {
 
   /**
-   * Implements BlockInterface::access().
+   * Overrides \Drupal\block\BlockBase::access().
    */
   public function access() {
-    global $user;
-    return (!$user->uid && !(arg(0) == 'user' && !is_numeric(arg(1))));
+    return (!$GLOBALS['user']->uid && !(arg(0) == 'user' && !is_numeric(arg(1))));
   }
 
   /**
-   * Implements BlockInterface::build().
+   * Overrides \Drupal\block\BlockBase::build().
    */
   public function build() {
     $form = drupal_get_form('user_login_form');
@@ -58,4 +64,5 @@ public function build() {
       ),
     );
   }
+
 }
diff --git a/core/modules/user/lib/Drupal/user/Plugin/block/block/UserNewBlock.php b/core/modules/user/lib/Drupal/user/Plugin/block/block/UserNewBlock.php
index 33da17e..f75c070 100644
--- a/core/modules/user/lib/Drupal/user/Plugin/block/block/UserNewBlock.php
+++ b/core/modules/user/lib/Drupal/user/Plugin/block/block/UserNewBlock.php
@@ -1,5 +1,10 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\user\Plugin\block\block\UserNewBlock.
+ */
+
 namespace Drupal\user\Plugin\block\block;
 
 use Drupal\block\BlockBase;
@@ -7,6 +12,8 @@
 use Drupal\Core\Annotation\Translation;
 
 /**
+ * @todo.
+ *
  * @Plugin(
  *   id = "user_new_block",
  *   subject = @Translation("Who's new"),
@@ -16,7 +23,7 @@
 class UserNewBlock extends BlockBase {
 
   /**
-   * Implements BlockInterface::settings().
+   * Overrides \Drupal\block\BlockBase::settings().
    */
   public function settings() {
     return array(
@@ -28,14 +35,14 @@ public function settings() {
   }
 
   /**
-   * Implements BlockInterface::access().
+   * Overrides \Drupal\block\BlockBase::access().
    */
   public function access() {
     return user_access('access content');
   }
 
   /**
-   * Implements BlockInterface::configure().
+   * Overrides \Drupal\block\BlockBase::configure().
    */
   public function configure($form, &$form_state) {
     $form['user_block_whois_new_count'] = array(
@@ -48,14 +55,14 @@ public function configure($form, &$form_state) {
   }
 
   /**
-   * Implements BlockInterface::configureSubmit().
+   * Overrides \Drupal\block\BlockBase::configureSubmit().
    */
   public function configureSubmit($form, &$form_state) {
     $this->configuration['whois_new_count'] = $form_state['values']['user_block_whois_new_count'];
   }
 
   /**
-   * Implements BlockInterface::build().
+   * Overrides \Drupal\block\BlockBase::build().
    */
   public function build() {
     // Retrieve a list of new users who have subsequently accessed the site successfully.
@@ -69,4 +76,5 @@ public function build() {
     }
     return $build;
   }
+
 }
diff --git a/core/modules/user/lib/Drupal/user/Plugin/block/block/UserOnlineBlock.php b/core/modules/user/lib/Drupal/user/Plugin/block/block/UserOnlineBlock.php
index e38f1f8..f9d9245 100644
--- a/core/modules/user/lib/Drupal/user/Plugin/block/block/UserOnlineBlock.php
+++ b/core/modules/user/lib/Drupal/user/Plugin/block/block/UserOnlineBlock.php
@@ -1,5 +1,10 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\user\Plugin\block\block\UserOnlineBlock.
+ */
+
 namespace Drupal\user\Plugin\block\block;
 
 use Drupal\block\BlockBase;
@@ -7,6 +12,8 @@
 use Drupal\Core\Annotation\Translation;
 
 /**
+ * @todo.
+ *
  * @Plugin(
  *   id = "user_online_block",
  *   subject = @Translation("Who's online"),
@@ -15,8 +22,8 @@
  */
 class UserOnlineBlock extends BlockBase {
 
-    /**
-   * Implements BlockInterface::settings().
+  /**
+   * Overrides \Drupal\block\BlockBase::settings().
    */
   public function settings() {
     return array(
@@ -29,14 +36,14 @@ public function settings() {
   }
 
   /**
-   * Implements BlockInterface::access().
+   * Overrides \Drupal\block\BlockBase::access().
    */
   public function access() {
     return user_access('access content');
   }
 
   /**
-   * Implements BlockInterface::configure().
+   * Overrides \Drupal\block\BlockBase::configure().
    */
   public function configure($form, &$form_state) {
     $period = drupal_map_assoc(array(30, 60, 120, 180, 300, 600, 900, 1800, 2700, 3600, 5400, 7200, 10800, 21600, 43200, 86400), 'format_interval');
@@ -58,7 +65,7 @@ public function configure($form, &$form_state) {
   }
 
   /**
-   * Implements BlockInterface::configureSubmit().
+   * Overrides \Drupal\block\BlockBase::configureSubmit().
    */
   public function configureSubmit($form, &$form_state) {
     $this->configuration['seconds_online'] = $form_state['values']['user_block_seconds_online'];
@@ -66,9 +73,9 @@ public function configureSubmit($form, &$form_state) {
   }
 
   /**
-   * Implements BlockInterface::build().
+   * Overrides \Drupal\block\BlockBase::build().
    *
-   * @todo: Move this block to statistics.module and remove dependency on
+   * @todo Move this block to statistics.module and remove dependency on
    *   user.access.
    */
   public function build() {
diff --git a/core/modules/user/lib/Drupal/user/Tests/UserBlocksTests.php b/core/modules/user/lib/Drupal/user/Tests/UserBlocksTests.php
index c513d0e..a4458d4 100644
--- a/core/modules/user/lib/Drupal/user/Tests/UserBlocksTests.php
+++ b/core/modules/user/lib/Drupal/user/Tests/UserBlocksTests.php
@@ -21,6 +21,13 @@ class UserBlocksTests extends WebTestBase {
    */
   public static $modules = array('block');
 
+  /**
+   * The admin user used in this test.
+   *
+   * @var \Drupal\user\Plugin\Core\Entity\User
+   */
+  protected $adminUser;
+
   public static function getInfo() {
     return array(
       'name' => 'User blocks',
@@ -32,8 +39,8 @@ public static function getInfo() {
   function setUp() {
     parent::setUp();
 
-    $admin_user = $this->drupalCreateUser(array('administer blocks'));
-    $this->drupalLogin($admin_user);
+    $this->adminUser = $this->drupalCreateUser(array('administer blocks'));
+    $this->drupalLogin($this->adminUser);
 
     $block_id = 'user_login_block';
     $default_theme = variable_get('theme_default', 'stark');
@@ -48,7 +55,7 @@ function setUp() {
     $this->drupalPost('admin/structure/block/manage/' . $block_id . '/' . $default_theme, $block, t('Save block'));
     $this->assertText(t('The block configuration has been saved.'), 'User login block enabled');
     $this->plugin_id = 'plugin.core.block.' . $default_theme . '.' . $block['machine_name'];
-    $this->drupalLogout($admin_user);
+    $this->drupalLogout($this->adminUser);
   }
 
   /**
@@ -86,6 +93,10 @@ function testUserLoginBlock() {
    * Test the Who's Online block.
    */
   function testWhosOnlineBlock() {
+    $plugin_id = 'plugin.core.block.' . variable_get('theme_default', 'stark') . '.online';
+    $block = $this->container->get('plugin.manager.block')->getInstance(array('config' => $plugin_id));
+    $config = $block->getConfig();
+
     // Generate users.
     $user1 = $this->drupalCreateUser(array());
     $user2 = $this->drupalCreateUser(array());
@@ -95,19 +106,20 @@ function testWhosOnlineBlock() {
     $this->updateAccess($user1->uid);
     $this->updateAccess($user2->uid, REQUEST_TIME + 1);
 
-    // Insert an inactive user who should not be seen in the block.
-    $this->updateAccess($user3->uid, REQUEST_TIME - config('user.block')->get('seconds_online') - 1);
-
-    // Test block output. TODO. Needs to be changed once user login form has
-    // gotten some work.
-    //$block = user_block_view('online');
-    //$block['content'] = render($block['content']);
-    //$this->drupalSetContent($block['content']);
-    //$this->assertRaw(t('2 users'), 'Correct number of online users (2 users).');
-    //$this->assertText($user1->name, 'Active user 1 found in online list.');
-    //$this->assertText($user2->name, 'Active user 2 found in online list.');
-    //$this->assertNoText($user3->name, 'Inactive user not found in online list.');
-    //$this->assertTrue(strpos($this->drupalGetContent(), $user1->name) > strpos($this->drupalGetContent(), $user2->name), 'Online users are ordered correctly.');
+    // Insert an inactive user who should not be seen in the block, and ensure
+    // that the admin user used in setUp() does not appear.
+    $inactive_time = REQUEST_TIME - $config['seconds_online'] - 1;
+    $this->updateAccess($user3->uid, $inactive_time);
+    $this->updateAccess($this->adminUser->uid, $inactive_time);
+
+    // Test block output.
+    $content = $block->build();
+    $this->drupalSetContent(render($content));
+    $this->assertRaw(t('2 users'), 'Correct number of online users (2 users).');
+    $this->assertText($user1->name, 'Active user 1 found in online list.');
+    $this->assertText($user2->name, 'Active user 2 found in online list.');
+    $this->assertNoText($user3->name, 'Inactive user not found in online list.');
+    $this->assertTrue(strpos($this->drupalGetContent(), $user1->name) > strpos($this->drupalGetContent(), $user2->name), 'Online users are ordered correctly.');
   }
 
   /**
diff --git a/core/modules/views/lib/Drupal/views/Plugin/Derivative/ViewsBlock.php b/core/modules/views/lib/Drupal/views/Plugin/Derivative/ViewsBlock.php
index 8a3abb0..45db464 100644
--- a/core/modules/views/lib/Drupal/views/Plugin/Derivative/ViewsBlock.php
+++ b/core/modules/views/lib/Drupal/views/Plugin/Derivative/ViewsBlock.php
@@ -10,12 +10,14 @@
 use Drupal\Component\Plugin\Derivative\DerivativeInterface;
 
 /**
- * @todo.
+ * Provides block plugin definitions for all Views block displays.
  */
 class ViewsBlock implements DerivativeInterface {
 
   /**
-   * @todo.
+   * List of derivative definitions.
+   *
+   * @var array
    */
   protected $derivatives = array();
 
diff --git a/core/modules/views/lib/Drupal/views/Plugin/Derivative/ViewsExposedFilterBlock.php b/core/modules/views/lib/Drupal/views/Plugin/Derivative/ViewsExposedFilterBlock.php
index 98e67bd..f0408f9 100644
--- a/core/modules/views/lib/Drupal/views/Plugin/Derivative/ViewsExposedFilterBlock.php
+++ b/core/modules/views/lib/Drupal/views/Plugin/Derivative/ViewsExposedFilterBlock.php
@@ -1,14 +1,28 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\views\Plugin\Derivative\ViewsExposedFilterBlock.
+ */
+
 namespace Drupal\views\Plugin\Derivative;
 
 use Drupal\Component\Plugin\Derivative\DerivativeInterface;
 
+/**
+ * Provides block plugin definitions for all Views exposed filters.
+ */
 class ViewsExposedFilterBlock implements DerivativeInterface {
+
+  /**
+   * List of derivative definitions.
+   *
+   * @var array
+   */
   protected $derivatives = array();
 
   /**
-   * Implements DerivativeInterface::getDerivativeDefinition().
+   * Implements \Drupal\Component\Plugin\Derivative\DerivativeInterface::getDerivativeDefinition().
    */
   public function getDerivativeDefinition($derivative_id, array $base_plugin_definition) {
     if (!empty($this->derivatives) && !empty($this->derivatives[$derivative_id])) {
@@ -19,7 +33,7 @@ public function getDerivativeDefinition($derivative_id, array $base_plugin_defin
   }
 
   /**
-   * Implements DerivativeInterface::getDerivativeDefinitions().
+   * Implements \Drupal\Component\Plugin\Derivative\DerivativeInterface::getDerivativeDefinitions().
    */
   public function getDerivativeDefinitions(array $base_plugin_definition) {
     foreach (views_get_all_views() as $view) {
@@ -45,4 +59,5 @@ public function getDerivativeDefinitions(array $base_plugin_definition) {
     }
     return $this->derivatives;
   }
+
 }
diff --git a/core/modules/views/lib/Drupal/views/Plugin/block/block/ViewsBlock.php b/core/modules/views/lib/Drupal/views/Plugin/block/block/ViewsBlock.php
index 1bd243f..5b7a26e 100644
--- a/core/modules/views/lib/Drupal/views/Plugin/block/block/ViewsBlock.php
+++ b/core/modules/views/lib/Drupal/views/Plugin/block/block/ViewsBlock.php
@@ -2,7 +2,7 @@
 
 /**
  * @file
- * Contains Drupal\views\Plugin\block\block\ViewsBlock.
+ * Contains \Drupal\views\Plugin\block\block\ViewsBlock.
  */
 
 namespace Drupal\views\Plugin\block\block;
@@ -13,6 +13,8 @@
 use Drupal\Component\Plugin\Discovery\DiscoveryInterface;
 
 /**
+ * @todo.
+ *
  * @Plugin(
  *   id = "views_block",
  *   subject = @Translation("Views Block"),
@@ -23,29 +25,30 @@
 class ViewsBlock extends BlockBase {
 
   /**
-   * @todo.
+   * The View executable object.
+   *
+   * @var \Drupal\views\ViewExecutable
    */
   protected $view;
 
   /**
-   * @todo.
+   * The display ID being used for this View.
+   *
+   * @var string
    */
-  protected $display_id;
+  protected $displayID;
 
   /**
    * Overrides \Drupal\Component\Plugin\PluginBase::__construct().
    */
   public function __construct(array $configuration, $plugin_id, DiscoveryInterface $discovery) {
     parent::__construct($configuration, $plugin_id, $discovery);
-    list($plugin, $delta) = explode(':', $this->getPluginId());
-
-    $start = microtime(TRUE);
 
-    list($name, $display_id) = explode('-', $delta, 2);
-    $this->display_id = $display_id;
-    // Load the view
+    list($plugin, $delta) = explode(':', $this->getPluginId());
+    list($name, $this->displayID) = explode('-', $delta, 2);
+    // Load the view.
     $this->view = views_get_view($name);
-    $this->view->setDisplay($display_id);
+    $this->view->setDisplay($this->displayID);
   }
 
   /**
@@ -64,17 +67,17 @@ public function configureWrapper($form, &$form_state) {
    * Overrides \Drupal\block\BlockBase::access().
    */
   public function access() {
-    return $this->view->access($this->display_id);
+    return $this->view->access($this->displayID);
   }
 
   /**
    * Overrides \Drupal\block\BlockBase::build().
    */
   public function build() {
-    $output = $this->view->executeDisplay($this->display_id);
+    $output = $this->view->executeDisplay($this->displayID);
     // Before returning the block output, convert it to a renderable array
     // with contextual links.
-    views_add_block_contextual_links($output, $this->view, $this->display_id);
+    views_add_block_contextual_links($output, $this->view, $this->displayID);
     $this->view->destroy();
     return $output;
   }
diff --git a/core/modules/views/lib/Drupal/views/Plugin/block/block/ViewsExposedFilterBlock.php b/core/modules/views/lib/Drupal/views/Plugin/block/block/ViewsExposedFilterBlock.php
index ef9feae..e172e05 100644
--- a/core/modules/views/lib/Drupal/views/Plugin/block/block/ViewsExposedFilterBlock.php
+++ b/core/modules/views/lib/Drupal/views/Plugin/block/block/ViewsExposedFilterBlock.php
@@ -1,11 +1,18 @@
 <?php
 
+/**
+ * @file
+ * Contains \Drupal\views\Plugin\block\block\ViewsExposedFilterBlock.
+ */
+
 namespace Drupal\views\Plugin\block\block;
 
 use Drupal\Core\Annotation\Plugin;
 use Drupal\Core\Annotation\Translation;
 
 /**
+ * @todo.
+ *
  * @Plugin(
  *   id = "views_exposed_filter_block",
  *   subject = @Translation("Views Exposed Filter Block"),
@@ -16,7 +23,7 @@
 class ViewsExposedFilterBlock extends ViewsBlock {
 
   /**
-   * Implements BlockInterface::build().
+   * Overrides \Drupal\block\BlockBase::build().
    */
   public function build() {
     $type = 'exp';
@@ -27,4 +34,5 @@ public function build() {
     $this->view->destroy();
     return $output;
   }
+
 }
diff --git a/core/profiles/testing/config/plugin.core.block.stark.online.yml b/core/profiles/testing/config/plugin.core.block.stark.online.yml
new file mode 100644
index 0000000..3b3f5c5
--- /dev/null
+++ b/core/profiles/testing/config/plugin.core.block.stark.online.yml
@@ -0,0 +1,23 @@
+id: user_online_block
+properties:
+  administrative: '1'
+seconds_online: '900'
+max_list_count: '10'
+status: '1'
+cache: '-1'
+subject: 'Who''s online'
+visibility:
+  path:
+    visibility: '0'
+    pages: ''
+  role:
+    roles: {  }
+  node_type:
+    types:
+      article: '0'
+      page: '0'
+      poll: '0'
+  visibility__active_tab: edit-visibility-path
+module: user
+region: sidebar_first
+weight: '0'