public function addFile($name, $label = '', $is_mandatory = true)
    {
        $e = new \FrenchFrogs\Form\Element\File($name, $label);
        $this->addElement($e);

        if ($is_mandatory) {
            $e->addRule('required');
        } else {
            $e->addFilter('nullable');
        }

        return $e;
    }