Merge branch '4.4'

* 4.4:
  fixup
  tweak #13099
  Update service_subscribers_locators.rst

Author: HeahDude

service_container/service_subscribers_locators.rst

@@ -515,7 +515,7 @@ attribute to the locator service defining the name of this custom method:
             # ...
 
             App\HandlerCollection:
-                arguments: [!tagged_locator { tag: 'app.handler', default_index_method: 'myOwnMethodName' }]
+                arguments: [!tagged_locator { tag: 'app.handler', index_by: 'key', default_index_method: 'myOwnMethodName' }]
 
     .. code-block:: xml
 
@@ -531,7 +531,7 @@ attribute to the locator service defining the name of this custom method:
                 <!-- ... -->
 
                 <service id="App\HandlerCollection">
-                    <argument type="tagged_locator" tag="app.handler" default-index-method="myOwnMethodName"/>
+                    <argument type="tagged_locator" tag="app.handler" index-by="key" default-index-method="myOwnMethodName"/>
                 </service>
             </services>
         </container>
@@ -544,10 +544,16 @@ attribute to the locator service defining the name of this custom method:
         return function(ContainerConfigurator $configurator) {
             $configurator->services()
                 ->set(App\HandlerCollection::class)
-                    ->args([tagged_locator('app.handler', null, 'myOwnMethodName')])
+                    ->args([tagged_locator('app.handler', 'key', 'myOwnMethodName')])
             ;
         };
 
+.. note::
+
+    Since code should not be responsible for defining how the locators are
+    going to be used, a configuration key (``key`` in the example above) must
+    be set so the custom method may be called as a fallback.
+
 Service Subscriber Trait
 ------------------------