public function addGroup($label = null)
    {
        if (!is_array($label)) {
            $label = ['label' => $label];
        } elseif (isset($label[0])) {
            $label['label'] = $label[0];
            unset($label[0]);
        }

        $label['form'] = $this->form;

        return $this->add(new static($label));
    }