If you use some character - like <, > or " - in the help line text for a custom BBcode, the tooltip text displayed - when the mouse moves over its BBcode button - will be unreadable in the posting editor. See attached screenshots.

The problem is due to that code in posting_buttons.html template file

title="{{ custom_tags.BBCODE_HELPLINE|e('html_attr') }}"

The escape ('html_attr') seems to useless and even counterproductive. Here is the HTML output for the help line texts of screenshots.

title="Same effect as &lt&#x3B;del&gt&#x3B; or &lt&#x3B;s&gt&#x3B; HTML tags"

title="Same effect as &quot&#x3B;del&quot&#x3B; or &quot&#x3B;s&quot&#x3B; HTML tags"

A simpler title="{custom_tags.BBCODE_HELPLINE}" is enough. Here is the HTML output:

title="Same effect as <del> or <s> HTML tags"

title="Same effect as "del" or "s" HTML tags"

<, > or " turn into to &lt;, &gt; or &quot;

Therefore, there is no potential problem.