$re = '/(\d+[a-z]?\.)?[ ]?(.*)/';
$str = '11a. A numbered agenda item
Unnumbered agenda item
12. Another numbered agenda item
Another UNnumbered agenda item
13. A numbered agenda item
';
preg_match_all($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