protected function renderBackendView($start, NavigationIterator $iterator = null): string
    {
        $parent = $this->getParent();

        return $this->render(
            new ToolkitTemplateReference(
                'be_bs_tab',
                'html5',
                ToolkitTemplateReference::SCOPE_BACKEND
            ),
            [
                'name'  => $parent ? $parent->bs_tab_name : null,
                'color' => $start ? $this->rotateColor('ce:' . $start->id) : null,
                'error' => $start ? null : $this->translator->trans('ERR.bsTabParentMissing', [], 'contao_default'),
                'title' => $iterator ? $iterator->currentTitle() : null,
            ]
        );
    }