Knockout-Lite/app/BbCode/Tag/Spoiler.php

<?php

namespace App\BbCode\Tag;

use Knockout\BbCode\Tag\SimpleTag;

class Spoiler extends SimpleTag
{

    public function getCloseHtmlTag(): string
    {
        return '</span>';
    }

    public function getOpenHtmlTag(): string
    {
        return '<span class="spoiler">';
    }

    public function getTag() : string
    {
        return 'spoiler';
    }
}