src/TwbBundle/Form/View/Helper/TwbBundleForm.php
public function openTag(FormInterface $form = null)
    {
        $this->setFormClass($form, $this->formLayout);
        return parent::openTag($form);
    }
public function openTag(FormInterface $form = null)
    {
        $this->setFormClass($form, $this->formLayout);
        return parent::openTag($form);
    }
Generate an opening form tag
@param null|FormInterface $form
@return string