Multiple choice in Bitrix?

Question

1C-Bitrix

Bitrix has a gallery
Categories in it are displayed in the template in this way

<ul>
        <? foreach ($arResult["SECTIONS"] as $arSection) { ?>
            <li><a href="#" data-toggle=".sec-<?= $arSection['ID'] ?>"><?= $arSection['NAME'] ?></a></li>
        <? } ?>
    </ul>

The problem is that you can select several categories at once. And you only need one. Where to dig?