How to copy content of element and place it into another element? - php

Question

Example file:
<p>
some content
<sup>3</sup>
some content</p>
<p>
some content
<sup>4</sup>
some content<sup>5</sup></p>
<div class="footnote">
<li id="fn3">
<p>
content3
↩
</p>
</li>
<li id="fn4">
<p>
content4
↩
</p>
</li>
<li id="fn5">
<p>
content5
↩
</p>
</li>
<div>
I need to place reference footnote at the bottom of the paragraph where the footnote is referenced.(i.e.)if the content in ptag has aelement with class fn-ref(one or many atags in a paragraph), I need to place related footnote at the bottom of that paragraph. Related footnote reference can be found in the div class="footnotes"
I should search in every ptag for a class="fn-ref", If I found, I should create a div class="footnote" in which the related footnote reference content should be placed. If it is more than one, then within that div element itself reference content should be placed one by one.
Expected output:
<p>
some content
<sup>3</sup>
some content</p>
<div class=footnote>
<p>
<span class="label-fn">
3
</span>
content3
</p>
</div>
<p>
some content
<sup>4</sup>
some content<sup>5</sup></p>
<div class=footnote>
<p>
<span class="label-fn">
4
</span>
content4
</p>
<p>
<span class="label-fn">
5
</span>
content5
</p>
</div>
I should try like parent().clone().html() then before and after add stuff but I don't know where to get started as am newbie in DOM parser class.
Tried so far:
$dom = new DOMDocument;
$dom->loadHTMLFile("test.html", LIBXML_HTML_NOIMPLIED | LIBXML_HTML_NODEFDTD);
$xp = new DOMXPath($dom);
$xp->registerNamespace("php", "http://php.net/xpath");
$pElement = $xp->query("//*[contains(#class, "fn-ref")]");
foreach($pElement as $pNode) {
if ($pNode->nodeName[0] === 'p') {
//??