How to make a regulak for html-lists?

Question

PHP

<p>There is some html code where tags can be different instead . For example:

<p>Some text</p>
<li>first list element</li>
<li>second list</li>
<p>Some text 2</p>
<p>Some text 3</p>
<li>first list element 2</li>
<li>second list element 2</li>
<h2>header 2</h2>

Help me compose a regular expression for preg_match (PHP) to select all the text from the first <li>to the last </li>in the list and wrap it in <ul> </ul>
That is, in fact, so that the output html code looks like:

<p>Some text</p>
<ul>
<li>first list element</li>
<li>second list</li>
</ul>
<p>Some text 2</p>
<p>Some text 3</p>
<ul>
<li>first list element 2</li>
<li>second list element 2</li>
</ul>
<h2>header 2</h2>

If it's easier to do it not through RegEx, it will be great)

Answer 1

$str = "html";
$pattern = "/((<li>(.*?)<\/li>\s*)+)/s";

echo preg_replace($pattern, "<ul>$0</ul>", $str);