Merge branch '3.4' into 4.4

* 3.4:
  Added: Missing comment on XML and PHP code-block

Author: javiereguiluz

service_container/service_decoration.rst

@@ -148,9 +148,9 @@ automatically changed to ``decorating_service_id + '.inner'``):
                 <service id="App\DecoratingMailer"
                     decorates="App\Mailer"
                 >
+                    <!-- pass the old service as an argument -->
                     <argument type="service" id="App\DecoratingMailer.inner"/>
                 </service>
-
             </services>
         </container>
 
@@ -173,7 +173,6 @@ automatically changed to ``decorating_service_id + '.inner'``):
                 ->args([ref(DecoratingMailer::class.'.inner')]);
         };
 
-
 .. tip::
 
     The visibility of the decorated ``App\Mailer`` service (which is an alias