- htmlentities: documentation ( source)
<?php
$xml_header = "<?xml version='1.0' encoding='utf-8'?><xml/>";
$xml = new SimpleXMLElement($xml_header);
$xml->addChild("first_string","this is &lt;mystring> &euro; &gt; $");
$xml->addChild("second_string",htmlentities("this is <mystring> € > $"));
echo $xml->first_string . $xml->second_string;