feature #8522 Add GroupSequence validation_groups capability doc (damienalexandre, javiereguiluz)

This PR was merged into the 2.7 branch.

Discussion
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Add GroupSequence validation_groups capability doc

When using form types without object, we often define constraints in the form itself.

I missed a way to use the sequential groups without object, but already implemented, so here is the documentation for it 😋

Cheers.

Commits
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9eb4b11 Minor syntax issues
39f9143 Fix code-block
6ad18f2 Add GroupSequence validation_groups capability doc

Author: weaverryan

validation/sequence_provider.rst

@@ -140,6 +140,23 @@ that group are valid, the second group, ``Strict``, will be validated.
     sequence, which will contain the ``Default`` group which references the
     same group sequence, ...).
 
+You can also define a group sequence in the ``validation_groups`` form option::
+
+    use Symfony\Component\Validator\Constraints\GroupSequence;
+    use Symfony\Component\Form\AbstractType;
+    // ...
+    
+    class MyType extends AbstractType
+    {
+        // ...
+        public function configureOptions(OptionsResolver $resolver)
+        {
+            $resolver->setDefaults([
+                'validation_groups' => new GroupSequence(['First', 'Second']),
+            ]);
+        }
+    }
+
 Group Sequence Providers
 ------------------------