15874 add note about importance off order

Author: JohJohan

reference/configuration/framework.rst

@@ -3372,6 +3372,24 @@ Defines what ``log_level`` and ``status_code`` should be returned by exception c
             ;
         };
 
+.. note::
+
+    When defining exceptions the order is important as it will use the first exception that matches ``instanceof``
+
+Example with ``\RuntimeException`` and ``\Exception``:
+
+.. code-block:: yaml
+
+        # config/packages/exceptions.yaml
+        framework:
+            exceptions:
+                Exception:
+                    log_level: debug
+                    status_code: 404
+                RuntimeException: # This will never be used as \RuntimeException extends \Exception
+                    log_level: debug
+                    status_code: 422
+
 .. _`HTTP Host header attacks`: https://www.skeletonscribe.net/2013/05/practical-http-host-header-attacks.html
 .. _`Security Advisory Blog post`: https://symfony.com/blog/security-releases-symfony-2-0-24-2-1-12-2-2-5-and-2-3-3-released#cve-2013-4752-request-gethost-poisoning
 .. _`Doctrine Cache`: https://www.doctrine-project.org/projects/doctrine-cache/en/current/index.html