diff --git a/core/modules/system/core.api.php b/core/modules/system/core.api.php
index 2f951fe..daa46e3 100644
--- a/core/modules/system/core.api.php
+++ b/core/modules/system/core.api.php
@@ -712,15 +712,16 @@
  * The Services and Dependency Injection Container concepts have been adopted by
  * Drupal from the @link http://symfony.com/ Symfony framework. @endlink A
  * "service" (such as accessing the database, sending email, or translating user
- * interface text) is defined (given an name and an interface), and a default
- * class is defined to provide the service. These two steps must be done
- * together, and can be done by Drupal Core or a module. Other modules can then
- * define alternative classes to provide the same services, overriding the
- * default classes. Classes and functions that need to use the service should
- * always instantiate the class via the dependency injection container (also
- * known simply as the "container"), rather than instantiating a particular
- * service provider class directly, so that they get the correct class
- * (default or overridden).
+ * interface text) is defined (given an name and an interface or at least a
+ * class that defines the methods that may be called), and a default class is
+ * defined to provide the service. These two steps must be done together, and
+ * can be done by Drupal Core or a module. Other modules can then define
+ * alternative classes to provide the same services, overriding the default
+ * classes. Classes and functions that need to use the service should always
+ * instantiate the class via the dependency injection container (also known
+ * simply as the "container"), rather than instantiating a particular service
+ * provider class directly, so that they get the correct class (default or
+ * overridden).
  *
  * See https://drupal.org/node/2133171 for more detailed information on
  * services and the dependency injection container.
@@ -738,7 +739,8 @@
  *   class: Drupal\Core\Path\AliasManager
  *   arguments: ['@path.crud', '@path.alias_whitelist', '@language_manager']
  * @endcode
- * Some services use factory classes; a typical service definition is:
+ * Some services use other services as factories; a typical service definition
+ * is:
  * @code
  *   cache.entity:
  *     class: Drupal\Core\Cache\CacheBackendInterface