REGEX to find all links with the class of "demo" that do not have a </i> preceding the </a>

gistfile1.php

<?php

$content = '<div class="actions">
  <a href="http://davidwalsh.name/demo/folding-animation.php" class="demo">Some text<i class="something"></i></a>
  <a href="http://davidwalsh.name/demo/folding-animation.php" class="demo">Some other text</a>
  <div class="clear"></div>
</div>';

$results = preg_replace('/(<a\s+.*?class="demo".*?)((?<!<\/i>)<\/a>)/i', '${1}<i class="something"></i></a>', $content);

echo $results;