$re = '/(^.*btn.*clickable.*$)|(^.*clickable.*btn.*$)/m';
$str = '<div class="clickable"></div>
<div class="btn clickable"></div>
<div class="clickable btn"></div>
<div class="btn btn-default clickable"></div>
<div class="clickable addButton"></div>
<div class="btn js-clickable"></div>
<div class="modalButton btn btn-primary addAction clickable"></div>';
preg_match_all($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