> In PHP 5.3.4 and later, self-closing XHTML tags are ignored and only non-self-closing tags should be used in allowable_tags. For example, to allow both <br> and <br/>, you should use:
> ```php
> <?php
> strip_tags($input, '<br>');
> ?>
> ```

Ref:
* https://www.php.net/manual/en/function.strip-tags.php#refsect1-function.strip-tags-changelog