<?php
$str = '<div style="float:left" id="ab">123213</div><div class="a123">213123</div>';
$search = '#<[a-zA-Z0-9][^>]+?id=[^>]+?>.*?</div>#is';
preg_match_all($search,$str,$r);
echo '<pre>';
print_r($r);
echo '</pre>';
?>
Array
(
[0] => Array
(
[0] => <div style="float:left" id="ab">123213</div>
)
)
