Symfony\Component\Form\FieldGroup::getFieldsByVisibility PHP Method

    protected function getFieldsByVisibility($hidden, $recursive)
    {
        $fields = array();
        $hidden = (bool)$hidden;

        foreach ($this->fields as $field) {
            if ($field instanceof FieldGroup && $recursive) {
                $fields = array_merge($fields, $field->getFieldsByVisibility($hidden, $recursive));
            } else if ($hidden === $field->isHidden()) {
                $fields[] = $field;
            }
        }

        return $fields;
    }