我的Codeigniter文件说

$CI->output->set_header("Access-Control-Allow-Origin: *");
$CI->output->set_header("Access-Control-Expose-Headers: Access-Control-Allow-Origin");
$CI->output->set_status_header(200);
$CI->output->set_content_type('application/json');
echo json_encode(array("city" => "dhaka"));

但是我得到的http响应是：

Request URL:http://localhost/index.php/location/city
Request Method:POST
Status Code:200 OK

Connection:Keep-Alive
Content-Length:16
Content-Type:text/html
Date:Sun, 22 Jul 2012 10:27:32 GMT
Keep-Alive:timeout=5, max=100
Server:Apache/2.2.21 (Unix) mod_ssl/2.2.21 OpenSSL/0.9.8r DAV/2 PHP/5.3.6
X-Powered-By:PHP/5.3.6

Access-Control-Allow-Origin即使包含，响应中仍缺少标题Access-Control-Expose-Headers: Access-Control-Allow- Origin。我有关此标头的信息来源来自Mozilla开发人员网站