$re = '/(?:<p class="credits">(<span class="contributors">)|(<\/span>)\1|\2<\/p>)/m';
$str = '<p class="credits"><span class="contributors">Writer – <a href="/contribs/001-John-Doe">J. Doe</a></span><span class="contributors">Producer – <a href="/contribs/002-Timothy-Smith">T. Smith</a></span><span class="contributors">Director – <a href="/contribs/003-Jane-Johnson">J. Johnson</a></span></p>
';
preg_match_all($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