$re = '/(?<=(?<!\S)\d+\.\s(?:\s\d+\.\s)*)[^\s.,:!?]+/m';
$str = '1. text
2. wordX wordY.
3. 4. wordZ.';
preg_match_all($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