yii\bootstrap\Nav::renderItems PHP Method

    public function renderItems()
    {
        $items = [];
        foreach ($this->items as $i => $item) {
            if (isset($item['visible']) && !$item['visible']) {
                continue;
            }
            $items[] = $this->renderItem($item);
        }
        return Html::tag('ul', implode("\n", $items), $this->options);
    }