How to solve the problem of closing tag first in php, for example, as follows

Unclosed tags will affect the layout of the original page when placed on the page for display. Therefore, after obtaining the data from the database, the unclosed tags must be closed before being placed on the page for display. So the question is: how to solve the problem of putting the end tag first? When the start tag comes after, for example:

Reply content:

Unclosed tags will affect the layout of the original page when placed on the page for display. Therefore, after obtaining the data from the database, the unclosed tags must be closed before being placed on the page for display. So the question is: how to solve the problem of putting the end tag first? When the start tag comes after, for example:

What is this

Use third-party tools to close tags
such as HTMLPurifier

How about this?

I am afraid that your idea cannot solve the problem. Such problems are often caused by abnormalities in the overall structure.
It means that there should be no html tags that span "blocks" when making templates, otherwise it will not only be difficult to maintain but also prone to problems. For example

<code>//a.php
<div>
    <h2>Hello</h2>
//b.php
    <p>world</p>
</div>
//c.php
require a.php;
require b.php;</code>

c combines a and b to form a completely closed label, but this is not recommended. Your idea is to close a and b respectively through algorithms, but this may invalidate the original css, resulting in abnormal layout, which means that the problem cannot be solved fundamentally. So I suggest you think carefully about the overall solution.

Regular match tag?