[#2963] Disabling validation corectly

Author: piorek

book/forms.rst

@@ -479,12 +479,10 @@ Disabling Validation
 .. versionadded:: 2.3
     The ability to set ``validation_groups`` to false was added in Symfony 2.3,
     although setting it to an empty array achieved the same result in previous
-    versions.
+    versions. Please note that empty array doesn't work anymore.
 
 Sometimes it is useful to suppress the validation of a form altogether. For
-these cases, you can skip the call to :method:`Symfony\\Component\\Form\\FormInterface::isValid`
-in your controller. If this is not possible, you can alternatively set the
-``validation_groups`` option to ``false`` or an empty array::
+these cases you can set the ``validation_groups`` option to ``false``::
 
     use Symfony\Component\OptionsResolver\OptionsResolverInterface;
 
@@ -497,9 +495,8 @@ in your controller. If this is not possible, you can alternatively set the
 
 Note that when you do that, the form will still run basic integrity checks,
 for example whether an uploaded file was too large or whether non-existing
-fields were submitted. If you want to suppress validation completely, remove
-the :method:`Symfony\\Component\\Form\\FormInterface::isValid` call from your
-controller.
+fields were submitted. If you want to surppress validation you can use 
+:ref:`POST_SUBMIT event <cookbook-dynamic-form-modification-supressing-form-validation>`
 
 .. index::
    single: Forms; Validation groups based on submitted data

cookbook/form/dynamic_form_modification.rst

@@ -535,3 +535,33 @@ after the sport is selected. This should be handled by making an AJAX call
 back to your application. In that controller, you can submit your form, but
 instead of processing it, simply use the submitted form to render the updated
 fields. The response from the AJAX call can then be used to update the view.
+
+.. _cookbook-dynamic-form-modification-supressing-form-validation:
+
+Supressing Form Validation
+---------------------------
+
+One way you can use ``POST_SUBMIT`` event is to completely supress 
+form validation. The reason for that is even if you set ``group_validation`` 
+to ``false`` there still some integrity check are run, for example whether 
+an uploaded file was too large or whether non-existing fields were submitted. 
+
+If you want to suppress even that, you should use ``POST_SUBMIT`` event to prevent 
+:class:`Symfony\\Component\\Form\\Extension\\Validator\\EventListener\\ValidationListener` 
+invocation::
+
+    use Symfony\Component\Form\FormBuilderInterface;
+    use Symfony\Component\Form\FormEvents;
+
+    public function buildForm(FormBuilderInterface $builder, array $options)
+    {
+        $builder->addEventListener(FormEvents::POST_SUBMIT, function($event) {
+            $event->stopPropagation();
+        }, /* priority higher than ValidationListener */ 200);
+
+        // ...
+    }
+
+Note that that by doing that you can disable something more than form validation, 
+because ``POST_SUBMIT`` event can be used for something else. 
+You also have to know what would be the right priority for disabling POST_SUBMIT events.