ie7 cross domain ajax request

gistfile1.txt

if ($.browser.msie && window.XDomainRequest && $.browser.version.toString().indexOf('7') == 0) {
    // Use Microsoft XDR
    var xdr = new XDomainRequest();
    xdr.open("get", url);
    xdr.onload = function () {
    var JSON = jQuery.parseJSON(xdr.responseText);
    if (JSON == null || typeof (JSON) == 'undefined')
    {
        JSON = jQuery.parseJSON(data.firstChild.textContent);
    }
        renderCommentCount(JSON);
    };
    xdr.send();
} else {
    jQuery.ajax({
        type: 'GET',
        url: url,
        processData: true,
        data: {},
        dataType: "json",
        success: function (data) { renderCommentCount(data); }
    });
}

window.XDomainRequest is undefined on IE7 ?

I thought XDR was only IE 8 and above