diff --git a/core/lib/Drupal/Core/Menu/ContextualLinkInterface.php b/core/lib/Drupal/Core/Menu/ContextualLinkInterface.php
index b1e566b..7ee9aef 100644
--- a/core/lib/Drupal/Core/Menu/ContextualLinkInterface.php
+++ b/core/lib/Drupal/Core/Menu/ContextualLinkInterface.php
@@ -34,7 +34,14 @@ public function getTitle();
   public function getRouteName();
 
   /**
-   * Returns the group this contextual link should be rendered on.
+   * Returns the group this contextual link should be rendered in.
+   *
+   * A contextual link group is a bunch of contextual link displayed together on
+   * the page. For example the block group displays all links related with the
+   * block, like the block instance edit link as well as the views edit link,
+   * if it is a view block.
+   *
+   * The name of a group has to be unique.
    *
    * @return string
    *   The contextual links group name.
diff --git a/core/lib/Drupal/Core/Menu/ContextualLinkManager.php b/core/lib/Drupal/Core/Menu/ContextualLinkManager.php
index 9851488..1ce55af 100644
--- a/core/lib/Drupal/Core/Menu/ContextualLinkManager.php
+++ b/core/lib/Drupal/Core/Menu/ContextualLinkManager.php
@@ -94,11 +94,11 @@ public function processDefinition(&$definition, $plugin_id) {
 
      // If there is no route name, this is a broken definition.
     if (empty($definition['route_name'])) {
-      throw new PluginException(sprintf('Plugin (%s) definition must include "route_name".', $plugin_id));
+      throw new PluginException(sprintf('Contextual link plugin (%s) definition must include "route_name".', $plugin_id));
     }
      // If there is no group name, this is a broken definition.
     if (empty($definition['group'])) {
-      throw new PluginException(sprintf('Plugin (%s) definition must include "group".', $plugin_id));
+      throw new PluginException(sprintf('Contextual link plugin (%s) definition must include "group".', $plugin_id));
     }
   }
 
@@ -133,7 +133,9 @@ public function getContextualLinkPluginsByGroup($group_name) {
    * @param string $group_name
    *   The group name.
    * @param array $route_parameters
-   *   The incoming route parameters.
+   *   The incoming route parameters. This route parameters need to have the
+   *   same name on all contextual link routes, e.g. you cannot use node and
+   *   entity in parallel.
    *
    * @return array
    *   A list of links as array, keyed by the plugin ID. Each entry is an
diff --git a/core/modules/contextual/contextual.module b/core/modules/contextual/contextual.module
index cee06c3..14e7249 100644
--- a/core/modules/contextual/contextual.module
+++ b/core/modules/contextual/contextual.module
@@ -335,8 +335,8 @@ function _contextual_links_to_id($contextual_links) {
   foreach ($contextual_links as $module => $args) {
     $group = $args[0];
     $route_parameters = drupal_http_build_query($args[1]);
-    $options = drupal_http_build_query((isset($args[2])) ? $args[2] : array());
-    $ids[] = "{$module}:{$group}:{$route_parameters}:{$options}";
+    $metadata = drupal_http_build_query((isset($args[2])) ? $args[2] : array());
+    $ids[] = "{$module}:{$group}:{$route_parameters}:{$metadata}";
   }
   return implode('|', $ids);
 }
@@ -356,12 +356,11 @@ function _contextual_id_to_links($id) {
   $contextual_links = array();
   $contexts = explode('|', $id);
   foreach ($contexts as $context) {
-    list($module, $parent_path, $args_raw, $metadata_raw) = explode(':', $context);
-    $path_args = array();
-    parse_str($args_raw, $path_args);
+    list($module, $group, $route_parameters_raw, $metadata_raw) = explode(':', $context);
+    parse_str($route_parameters_raw, $route_parameters);
     $metadata = array();
     parse_str($metadata_raw, $metadata);
-    $contextual_links[$module] = array($parent_path, $path_args, $metadata);
+    $contextual_links[$module] = array($group, $route_parameters, $metadata);
   }
   return $contextual_links;
 }
diff --git a/core/modules/system/system.api.php b/core/modules/system/system.api.php
index ca499cc..c1aed43 100644
--- a/core/modules/system/system.api.php
+++ b/core/modules/system/system.api.php
@@ -984,9 +984,9 @@ function hook_menu_contextual_links_alter(&$links, $router_item, $root_path) {
  * This hook is invoked by
  * \Drupal\Core\Menu\ContextualLinkManager::getContextualLinkPluginsByGroup().
  * The system-determined contextual links are passed in by reference. Additional
- * links may be added or existing links can be altered.
+ * links may be added and existing links can be altered.
  *
- * Each contextual link must at least contain:
+ * Each contextual link must contain at least:
  * - title: The localized title of the link.
  * - route_name: The route name of the link.
  * - route_parameters: The route parameters of the link.
@@ -998,10 +998,10 @@ function hook_menu_contextual_links_alter(&$links, $router_item, $root_path) {
  *   contextual links and must therefore be unique for each set of contextual
  *   links.
  * @param string $group
- *   The contextual links group name being requested.
+ *   The group of contextual links being rendered.
  * @param array $route_parameters.
  *   The route parameters passed to each route_name of the contextual links.
- *   So for example it is an array like that:
+ *   So e.g. it is an array like that:
  * @code
  *   node => $node->id().
  * @endcode
@@ -1010,10 +1010,10 @@ function hook_menu_contextual_links_alter(&$links, $router_item, $root_path) {
  */
 function hook_contextual_links_alter(array &$links, $group, array $route_parameters) {
   if ($group == 'menu') {
-    // Dynamically use the menu name for the title of the menu edit contextual
+    // Dynamically use the menu name for the title of the menu_edit contextual
     // link.
     $menu = \Drupal::entityManager()->getStorageController('menu')->load($route_parameters['menu']);
-    $links['menu_edit']['title'] = 'Edit menu: ' . $menu->label();
+    $links['menu_edit']['title'] = t('Edit menu: @label', array('@label' => $menu->label()));
   }
 }
 
@@ -1021,12 +1021,12 @@ function hook_contextual_links_alter(array &$links, $group, array $route_paramet
  * Alters the plugin definition of contextual links.
  *
  * @param array $contextual_links
- *   An array of contextual_links plugin definitions, keyed by plugin ID.
- *   Each entry contains the following keys:
+ *   An array of contextual_links plugin definitions, keyed by contextual link
+ *   ID. Each entry contains the following keys:
  *     - title: The displayed title of the link
  *     - route_name: The route_name of the contextual link to be displayed
  *     - group: The group under which the contextual links should be added to.
- *       Possible values are for example 'node' or 'menu'.
+ *       Possible values are e.g. 'node' or 'menu'.
  *
  * @see \Drupal\Core\Menu\ContextualLinkManager
  */
diff --git a/core/tests/Drupal/Tests/Core/Menu/ContextualLinkManagerTest.php b/core/tests/Drupal/Tests/Core/Menu/ContextualLinkManagerTest.php
index 15db4d5..4d7113e 100644
--- a/core/tests/Drupal/Tests/Core/Menu/ContextualLinkManagerTest.php
+++ b/core/tests/Drupal/Tests/Core/Menu/ContextualLinkManagerTest.php
@@ -164,7 +164,7 @@ public function testGetContextualLinkPluginsByGroup() {
   }
 
   /**
-   * Tests the getContextualLinkPluginsByGroup with a prefilled cache.
+   * Tests the getContextualLinkPluginsByGroup method with a prefilled cache.
    */
   public function testGetContextualLinkPluginsByGroupWithCache() {
     $definitions = array(
@@ -267,7 +267,7 @@ public function testGetContextualLinksArrayByGroup() {
       ->method('checkNamedRoute')
       ->will($this->returnValue(TRUE));
 
-    // Setup mocking of the plugin factory.
+    // Set up mocking of the plugin factory.
     $map = array();
     foreach ($definitions as $plugin_id => $definition) {
       $plugin = $this->getMock('Drupal\Core\Menu\ContextualLinkInterface');
@@ -336,7 +336,7 @@ public function testGetContextualLinksArrayByGroupAccessCheck() {
         array('test_route2', array('key' => 'value'), NULL, FALSE),
       )));
 
-    // Setup mocking of the plugin factory.
+    // Set up mocking of the plugin factory.
     $map = array();
     foreach ($definitions as $plugin_id => $definition) {
       $plugin = $this->getMock('Drupal\Core\Menu\ContextualLinkInterface');
diff --git a/core/vendor/phpunit/phpunit/PHPUnit/Framework/Comparator/Array.php b/core/vendor/phpunit/phpunit/PHPUnit/Framework/Comparator/Array.php
index d715514..ebbf928 100644
--- a/core/vendor/phpunit/phpunit/PHPUnit/Framework/Comparator/Array.php
+++ b/core/vendor/phpunit/phpunit/PHPUnit/Framework/Comparator/Array.php
@@ -165,7 +165,7 @@ public function assertEquals($expected, $actual, $delta = 0, $canonicalize = FAL
               $expString,
               $actString,
               FALSE,
-             'Failed asserting that two arrays are equal. ' . print_r(array_diff_assoc($expected, $actual), TRUE)
+             'Failed asserting that two arrays are equal.'
             );
         }
     }