$re = '/<span class="num">(?:\s+)?(?P<num>\d(?:\.\d{2}):?)/isu';
$str = '<h1>
<span class="paper-name">some string</span>
</h1>
<div class="data-row">
<span class="num">
0.25
</span>
</div>
<div class="data-row">
<span class="num">
0.25
</span>
</div>';
preg_match_all($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