get last 20 elements from sitemap.xml with php

example.php

<?php

// this is for schema http://www.sitemaps.org/schemas/sitemap/0.9

// config
$lastNElements = 20;

// url or filepath
//$source = 'https://www.digitec.ch/sitemap0.xml';

$source = <<<XML
<?xml version="1.0" encoding="UTF-8"?>
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9" xmlns:video="http://www.google.com/schemas/sitemap-video/1.1">
    <url>
        <loc>video post url/</loc>
        <video:video>
            <video:player_loc allow_embed="yes">yembed url/</video:player_loc>
            <video:title>TITLE</video:title>
            <video:description>DESCREPTIN</video:description>
            <video:thumbnail_loc>IMAGE.jpg</video:thumbnail_loc>
            <video:duration>384</video:duration>
        </video:video>
    </url>
</urlset>
XML;

// parsing
$xml = simplexml_load_string($source);
$xml->registerXPathNamespace('s', 'http://www.sitemaps.org/schemas/sitemap/0.9');

/**
 * //           = all nodes from current root
 * s            = defined namespace from below
 * url          = elements
 * positon()    = current node position
 * last()       = last node
 */

$xpath = '//s:url[position()>last()-'.$lastNElements.']';
foreach ($xml->xpath($xpath) as $element)
{
    print_r((string)$element->loc);
}