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

<?php

namespace App\BbCode\Tag;

use Knockout\BbCode\Tag\SimpleTag;

class Underline extends SimpleTag
{

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

    public function getOpenHtmlTag(): string
    {
        return '<u>';
    }

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