yii\grid\GridView::renderColumnGroup PHP Method

    public function renderColumnGroup()
    {
        $requireColumnGroup = false;
        foreach ($this->columns as $column) {
            /* @var $column Column */
            if (!empty($column->options)) {
                $requireColumnGroup = true;
                break;
            }
        }
        if ($requireColumnGroup) {
            $cols = [];
            foreach ($this->columns as $column) {
                $cols[] = Html::tag('col', '', $column->options);
            }
            return Html::tag('colgroup', implode("\n", $cols));
        } else {
            return false;
        }
    }