How To Extract Meta Tags Using DomDocument ?

Folks,

Using DomDocument, I am trying to build a crawler that, when I feed it a starting point url (initial url to start the crawling & link extracting from), it should navigate to the starting url and extract all the links found on the page.

<?php

$xml = file_get_contents($sitemapUrl); //Should I stick to this line or below line ?
// parse the sitemap content to object
$xml = simplexml_load_string($sitemapUrl); //Should I stick to this line or above line ?

$dom = new DOMDocument();
$dom->loadXML($xml);
if ($dom->nodeName === 'sitemapindex')
{
    //parse the index
    // retrieve properties from the sitemap object
    foreach ($xml->urlset as $urlElement) //Extracts html file urls.
    {
        // get properties
        $url = $urlElement->loc;
        $lastmod = $urlElement->lastmod;
        $changefreq = $urlElement->changefreq;
        $priority = $urlElement->priority;

        // print out the properties
        echo 'url: '. $url . '<br>';
        echo 'lastmod: '. $lastmod . '<br>';
        echo 'changefreq: '. $changefreq . '<br>';
        echo 'priority: '. $priority . '<br>';

        echo '<br>---<br>';
    }
} 
else if ($dom->nodeName === 'urlset')
{
    //parse url set
    // retrieve properties from the sitemap object
    foreach ($xml->sitemapindex as $urlElement) //Extracts Sitemap Urls.
    {
        // get properties
        $url = $urlElement->loc;
        $lastmod = $urlElement->lastmod;
        $changefreq = $urlElement->changefreq;
        $priority = $urlElement->priority;

        // print out the properties
        echo 'url: '. $url . '<br>';
        echo 'lastmod: '. $lastmod . '<br>';
        echo 'changefreq: '. $changefreq . '<br>';
        echo 'priority: '. $priority . '<br>';

        echo '<br>---<br>';
    }
} 

Now, how to write code to extract meta tags using DomDocument ?
Where can I find the code here ?
https://www.php.net/domdocument