jQuery，PHP，AJAX，“tu”变量beeing无缘无故发布，显示在var_dump（）中

Question

A jQuery AJAX request .post()s data to page.php, which creates $res and var_dump()s it.

$res:

$res = array(); 
foreach ($_REQUEST as $key => $value) {  
    if($key){ 
        $res[$key] = $value; 
    } 
} 

var_dump($res):

array(4) {
["text1"]=>  string(6) "mattis"
["text2"]=>  string(4) "test"
["tu"]=>  string(32) "deb6adbbff4234b5711cc4368c153bc4"
["PHPSESSID"]=> string(32) "cda24363cb9d3226bd37b2577ed0bc0b"
}

My javascript only sends text1 and text2:

$.post("page.php",{
   text1:"mattis",
   text2:"test"
}

What is the "tu" variable beeing sent? Apparantly it's very similar to the session id, but I've never seen it before.

EDIT: It is sent in IE but not in FF.

Answer 1

Since it isn't in the post data and there is no query string, it is probably stored in a cookie.

(Which, being set on a per-browser-instance basis, explains why it only appears in IE)