- str_repeat: documentation ( source)
<?php
$s2 = '<?xml version="1.0"?><!DOCTYPE kaboom [
<!ENTITY a "'.str_repeat('a', 1000).'">
]>
<kaboom>'.str_repeat('&a;', 1000).'</kaboom>';
$doc = new DOMDocument();
$doc->loadXML($s2);
echo strlen($doc->lastChild->nodeValue);