PHP - 解析 HTML，选择标签，在所选标签内插入另一个 HTML 字符串

Question

I am trying to insert HTML string inside another HTML element parsed in created DOM with loaded HTML from string;

Here is my code:

PHP:

$str = $attributes["description_text"]; // HTML string
$dom = new DOMDocument; // initialize the domdocument
$dom->loadHTML($str); // load our html into the $dom object
$items = $dom->getElementsByTagName('mark'); // retrieving elements by tag

$gear = $dom->createElement('a', "Lorem ipsum dolor sit amet");
$dom->appendChild($gear);
    
$output_dom = $dom->saveHTML();

return '<p>'. $output_dom .'</p>';

HTML ($str content):

Phasellus eu arcu vestibulum, ultrices massa eu, <mark>TOOLTIP</mark> sodales dui.

Desired Result ( a tag inside mark tag):

<p>Phasellus eu arcu vestibulum, ultrices massa eu, <mark>TOOLTIP<a>Lorem ipsum dolor sit amet</a></mark> sodales dui.</p>

Current Output:

<p>Phasellus eu arcu vestibulum, ultrices massa eu, <mark>TOOLTIP</mark> sodales dui.</p> 
<a>Lorem ipsum dolor sit amet</a>

So now new string appended in the end of whole paragraph, not inside mark tag

Answer 1

Found a solution, selected an item(0) from elements stored in $items , and called appendChild() on it, thanks to @NigelRen

$first_mark = $items->item(0);
$first_mark->appendChild($gear);