I'm trying to create a form with Symfony2 (v2.3.6) and take advantage of the autogenerated HTML5 constraints.

So, I created a very simple form with just one field with a `RegEx` constraint:

```
public function formAction()
{
    $form = $this->createFormBuilder()->add('animalName', 'text', array(
        'constraints' => new \Symfony\Component\Validator\Constraints\Regex('/(cat|dog)/')
    ))->getForm();

    if ($this->getRequest()->isMethod('POST')) {
        $form->bind($this->getRequest());
    }

    return $this->render('MeTestBundle:Default:form.html.twig', array('form' => $form->createView()));
}

```

And, in Twig, nothing out of the ordinary.

```
{% extends "::base.html.twig" %}

{% block body %}
    {{ form(form) }}
{% endblock %}

```

Well, as a final result, I was expecting `animalName` field to has a `pattern` attribute with value `(cat|dog)`. As it says in [this link](http://symfony.com/doc/current/reference/constraints/Regex.html#htmlpattern), Symfony would generate the `htmlPattern` of this constraint (I tested it, it returns `.*(cat|dog).*`, which is ok), and this attribute would be used on client side validation by using `pattern` HTML attribute on the `input` element. But there is no `pattern` attribute, the generated code is as follows:

```
<input type="text" id="form_animalName" name="form[animalName]" required="required" />

```

After a little research, I think that the responsible of guess the value of `pattern` attribute is `Symfony\Component\Form\Extension\Validator\ValidatorTypeGuesser`, but this service is never initialized (I wrote a `die` in it constructor and also forced the container to get the service to check if `die` is reached).

Am I missing something?