$re = '/^([1-9][9][0-9][0-9]|[2-9]\d{3})/m';
$str = '320x568
1920x1080
360600x640
1280x800
000x568
1920x1080
360x640
1280x800
1920x1080
480x800
320x480
1280x800
1900x1080
1366x768
000x768
1280x800
4000x2000
3000x2000
4080x4000
';
preg_match_all($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