这段代码检测浏览器Cookie是否打开，效果很好，可愣是没看懂

下面一段代码是检测浏览器Cookie是否打开，测试了IE6，IE7，Firefox3，safari, Opera9.5，测试结果都很正确，可就是没看懂？

function getCookieStatus() {

    var status ="Cookie关闭";

    var cookieStr = "wb_check=kcehc_bw";

    document.cookie = cookieStr;

if (document.cookie.indexOf(cookieStr) > -1) {
    status = "Cookie打开";
    var date = new Date();
    date.setTime(date.getTime() - 1000);
    document.cookie = cookieStr + "; expires=" + date.toGMTString();
}
return status;


}