Retriving content of the elements in a XML string
$xml = '<element_1>foobar</element_1>';

$dd = new DOMDocument();
$dd->loadXml($xml);

var_dump($dd->getElementsByTagName('element_1')); //this prints object(DOMNodeList)#2 (0) {
}

$xml = '<element_1>foobar</element_1>';

$dd = new DOMDocument();
$dd->loadXml($xml);

var_dump($dd->getElementsByTagName('element_1')->item(0)->nodeValue);
//string 'foobar' (length=6)

<?php

$xml = <<<XML
<?xml version='1.0'?>
<element_1>
foobar
</element_1>
XML;

$data = simplexml_load_string($xml);

echo $data;