$re = '/(\d\. (?:\D+|\d(?!\.))*)/';
$str = '1. first slice 2. second slice 3. slice number 3 4. the next one 5 that will not work but belong to no four 5. and this should be 5 and so one...
';
preg_match_all($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