$re = '~<IDOC BEGIN[^<]*(?:<(?!IDOC BEGIN)[^<]*?)*0007537181.*?</IDOC>~m';
$str = '<ORDERS>
<IDOC BEGIN><tag1>aaa</tag1><tag2>bbb</tag2><tag3>12345</tag3><tag4>ccc</tag4></IDOC>
<IDOC BEGIN><tag1>aaa</tag1><tag2>bbb</tag2><tag3>23456</tag3><tag4>ccc</tag4></IDOC>
<IDOC BEGIN><tag1>aaa</tag1><tag2>bbb</tag2><tag3>0007537181</tag3><tag4>ccc</tag4></IDOC>
<IDOC BEGIN><tag1>aaa</tag1><tag2>bbb</tag2><tag3>34567</tag3><tag4>ccc</tag4></IDOC>
</ORDER>';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
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