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symfony/framework-bundle/3.3/etc/packages/app.yaml

@@ -1,9 +1,16 @@
 services:
+    # default configuration for services in *this* file
     _defaults:
+        # automatically injects dependencies in your services
         autowire: true
+        # automatically registers your services as commands, form types, etc.
         autoconfigure: true
+        # this means you cannot fetch services directly from the container via $container->get()
+        # if you need to do this, you can override this setting on individual services
         public: false
 
+    # loads services from whatever directories you want (you can add directories!)
+    # this creates a service per class whose id is the fully-qualified class name
     App\:
         resource: '../../src/{Command,Form,EventSubscriber,Twig,Security}'