$re = '/<\?xml version="1\.0" encoding="UTF-8"\?>\s*<\s*([^\s]*)(?:.|\s)*<\/\s*\1\s*>/m';
$str = '--------------------------3cbec9ce8f05
Content-Disposition: form-data; name="owServerData"; filename="details.xml"
Content-Type: text/plain
<?xml version="1.0" encoding="UTF-8"?>
<Devices-Detail-Response xmlns="http://www.example.com"
<device>a</device>
<info>abc</info>
<test1><u>123</u><v>456</v><z/></test1>
</Devices-Detail-Response>
------------------------------3cbec9ce8f05--';
$subst = "";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php