$re = '/<tag1[^>]*>(.*?)<\/tag1>/';
$str = '<tag>
<tag1 class=1>data1</tag1>
<tag2 class=2>data2</tag2>
<tag1 class=3>data3</tag1>
</tag>';
preg_match($re, $str, $matches, PREG_OFFSET_CAPTURE, 0);
// Print the entire match result
var_dump($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