$re = '/{IF:(.*?)}[\s]*?(.*?)[\s]*?{ELSE}[\s]*?(.*?)[\s]*?{ENDIF}/i';
$str = '// Does NOT Work with html tags//
{IF:(!isset($_SESSION[\'loggedin\']))}
<div>
<p>This code no longer works</p>
<p>Remove this div and everything will work.</p>
</div>
{ELSE}
Bleh
{ENDIF}
';
preg_match($re, $str, $matches, PREG_OFFSET_CAPTURE, 0);
// Print the entire match result
var_dump($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