$re = '/^X\.(?:[3-9]|1[0-3])(?!\d)/m';
$str = 'X.2
X.3word
X.4w
X.5w
X.6w
X.7w
X.8w
X.9w
X.10w
X.11w
X.12w
X.13w
X.14';
preg_match_all($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