Collective\Html\FormBuilder::optionGroup PHP Method

    protected function optionGroup($list, $label, $selected)
    {
        $html = [];
        foreach ($list as $value => $display) {
            $html[] = $this->option($display, $value, $selected);
        }
        return $this->toHtmlString('<optgroup label="' . e($label) . '">' . implode('', $html) . '</optgroup>');
    }