diff --git a/core/lib/Drupal/Component/Plugin/Discovery/ProcessDecorator.php b/core/lib/Drupal/Component/Plugin/Discovery/ProcessDecorator.php
index 2e31dbc..bcb5cad 100644
--- a/core/lib/Drupal/Component/Plugin/Discovery/ProcessDecorator.php
+++ b/core/lib/Drupal/Component/Plugin/Discovery/ProcessDecorator.php
@@ -8,7 +8,10 @@
 namespace Drupal\Component\Plugin\Discovery;
 
 /**
- * Allows custom processing of the discovered definition..
+ * Allows custom processing of the discovered definition.
+ *
+ * Example use cases include adding in default values for a definition, or
+ * providing a backwards compatibility layer for renamed definition properties.
  */
 class ProcessDecorator implements DiscoveryInterface {
 
@@ -20,27 +23,27 @@ class ProcessDecorator implements DiscoveryInterface {
   protected $decorated;
 
   /**
-   * The processor function to run on each discovered definition.
+   * The processor callback to run on each discovered definition.
    *
    * @var callable
    */
-   protected $processFunction;
+   protected $processCallback;
 
   /**
    * Constructs a \Drupal\Component\Plugin\Discovery\ProcessDecorator object.
    *
    * @param \Drupal\Component\Plugin\Discovery\DiscoveryInterface $decorated
    *   The discovery object that is being decorated.
-   * @param callable $process_function
-   *   The processor function to run on each discovered definition. The
-   *   function will be called with the following arguments:
-   *   - array $definition: the discovered definition, that the function
+   * @param callable $process_callback
+   *   The processor callback to run on each discovered definition. The
+   *   callback will be called with the following arguments:
+   *   - array $definition: the discovered definition, that the callback
    *     should accept by reference and modify in place.
    *   - string $plugin_id: the corresponding plugin_id.
    */
-  public function __construct(DiscoveryInterface $decorated, $process_function) {
+  public function __construct(DiscoveryInterface $decorated, $process_callback) {
     $this->decorated = $decorated;
-    $this->processFunction = $process_function;
+    $this->processCallback = $process_callback;
   }
 
   /**
@@ -48,7 +51,9 @@ public function __construct(DiscoveryInterface $decorated, $process_function) {
    */
   public function getDefinition($plugin_id) {
     $definitions = $this->getDefinitions();
-    return isset($definitions[$plugin_id]) ? $definitions[$plugin_id] : NULL;
+    if (isset($definitions[$plugin_id])) {
+      return $definitions[$plugin_id];
+    }
   }
 
   /**
@@ -57,7 +62,7 @@ public function getDefinition($plugin_id) {
   public function getDefinitions() {
     $definitions = $this->decorated->getDefinitions();
     foreach ($definitions as $plugin_id => &$definition) {
-      call_user_func_array($this->processFunction, array(&$definition, $plugin_id));
+      call_user_func_array($this->processCallback, array(&$definition, $plugin_id));
     }
     return $definitions;
   }
@@ -68,4 +73,5 @@ public function getDefinitions() {
   public function __call($method, $args) {
     return call_user_func_array(array($this->decorated, $method), $args);
   }
+
 }