Fix doc

Author: bakura10

docs/07. Cookbook.md

@@ -316,22 +316,24 @@ class MustBeAuthorAssertion implements AssertionInterface
      * Check if this assertion is true
      *
      * @param  AuthorizationService $authorization
-     * @param  mixed                $context
+     * @param  mixed                $post
      *
      * @return bool
      */
-    public function assert(AuthorizationService $authorization, $context = null)
+    public function assert(AuthorizationService $authorization, $post = null)
     {
-        return $authorization->getIdentity() === $context->getAuthor();
+        return $authorization->getIdentity() === $post->getAuthor();
     }
 }
 ```
 
 This simple `MustBeAuthorAssertion` will check against the current `$authorization` if it equals the identity of the
-current context Author. Now `$context` may sound a little strange for now but let me make it clear. The `$context` is
-usually the object of interest. Imagine a user calls `http://my.dom/post/delete/42`, so obviously he wants to delete the
-Post-Entity with ID#42. In this case Entity#42 is our Context! If you're wondering of how the context get's there, bare
-with me, we will get to this later.
+current context Author. The second parameter is called the "context". A context can be anything (an object, a scalar,
+an array...) and makes only sense in the context of the assertion.
+
+Imagine a user calls `http://my.dom/post/delete/42`, so obviously he wants to delete the Post-Entity with ID#42. In
+this case Entity#42 is our Context! If you're wondering of how the context get there, bare with me, we will get to
+this later.
 
 Now that we have written the Assertion, we want to make sure that this assertion will always be called, whenever we
 check for the `deletePost` permission. We don't want others to delete our previous content! For this we have the so-