$re = '~(?s)(?<=<code>).*?(?=</code>)~';
$str = 'Loreum Ipsum Dolor Sit Amet <code>Some HTML Code like <h1>Head</h1></code>. Loreum Ipsum <code>Some Code</code> Dolor Sit Amet.';
preg_match_all($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