$re = '/(?\'number\'\d+)\t(?\'description\'.+?)(?=^\d|\Z)/ms';
$str = '# description
1 first item
2 second ite3m on two or
more lines of text
3 third item';
preg_match_all($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