public function vendorDir(
        string $type,
        string $append = '',
        string $form = ''
    ): string {
        $rel_dir = \explode('/', $this->relativeDir());
        $vendor = \reset($rel_dir) ?: 'vendor';

        return 'relative' === $form ?
            "{$vendor}{$append}" :
            $this->themeDir($type, "/{$vendor}{$append}");
    }