$re = '/<li>(?:(?!<\/li>).)*(THE WORDS).*?<\/li>/s';
$str = '<li>hello
fhgg
hgfhgvh
hgjh
jhhj
THE WORDS
</li>
<li> cruel </li>
<li> world THE WORDS </li>';
preg_match_all($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