<?php
$value = "<div>dies ist ein test</div><div>";
$dom = new DOMDocument();
@$dom->loadHTML('<?xml encoding="utf-8" ?>'.$value, LIBXML_HTML_NODEFDTD);
// Fix the html errors
$value = $dom->saveHtml($dom->getElementsByTagName('body')->item(0));
// Remove body tag
$value = mb_strimwidth($value, 6, mb_strwidth($value, 'UTF-8') - 13, '', 'UTF-8');
echo $value;