$re = '/<li>[^<]*[Ss]izes[^<]*<\/li>/m';
$str = '<ul><li>Option to add embroidered text personalization below design<br/>for only $1.00 per shirt and free setup</li><li>Men's Sizes: XS-6XL</li><li>Individually folded and bagged with size sticker for easy distribution</li><li>Ready to ship in 7 business days after art approval</li></ul>
';
preg_match_all($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