Issue #2261391 by pwolanin, Crell: Fix up throws and other docs for FactoryInterface

core/lib/Drupal/Component/Plugin/Factory/FactoryInterface.php

 <?php
 /**
  * @file
- * Definition of Drupal\Component\Plugin\Factory\FactoryInterface.
+ * Contains \Drupal\Component\Plugin\Factory\FactoryInterface.
  */
 
 namespace Drupal\Component\Plugin\Factory;
@@ -12,15 +12,18 @@
 interface FactoryInterface {
 
   /**
-   * Returns a preconfigured instance of a plugin.
+   * Returns a pre-configured instance of a plugin.
    *
    * @param string $plugin_id
-   *   The id of the plugin being instantiated.
+   *   The ID of the plugin being instantiated.
    * @param array $configuration
    *   An array of configuration relevant to the plugin instance.
    *
    * @return object
    *   A fully configured plugin instance.
+   *
+   * @throws \Drupal\Component\Plugin\Exception\PluginException
+   *   If the instance cannot be created, such as if the ID is invalid.
    */
   public function createInstance($plugin_id, array $configuration = array());