For what server error code does the jquery ajax 'error' option stand for?

Question

Hi

Can someone tell me for what server request code does the 'error' option in jquery ajax ($.ajax) stand for? Because I want to handle the 400 server error, but I can't seem to do it using that 'error' option. I don't know if I'm doing something wrong in my code or whether it's a bug... Please I need your assistance. Thank you.

var options = {
    type: "post",
    target: "#responsePanel",
    beforeSend: function(){
        $("#uploadingImg").show();
        $("#polygonUploadPanel, #polygonUploadBtnHolder").hide();
    },
    complete: function(){
        $("#uploadingImg").hide();
        $("#polygonUploadPanel, #polygonUploadBtnHolder").show();
    },
    success: function(response, statusString, xhr, $form){
        $("#responsePanel").html(statusString);
        //map.polygonUploaded();
        $("#polygonUploadForm").hide();
    },
    error: function(response, statusString, err){
        $("#responsePanel").html(statusString);
        $("#polygonUploadPanel, #polygonUploadBtnHolder").hide();
        $("#polygonUploadBtn").hide();
        $("#ajaxUploadError").show();
        $(".errorHeading a").click(function(e){
            if($(".errorDetails").is(":visible")){
                $(".errorDetails").hide();
            }
            else{
                $(".errorDetails").show();
            }
        });

        if(response.status == 400) {
             $("#polygonUploadForm").show();
        }

        if(response.status == 601) {
             sessionTimedOut();
        }
    }
};
$.ajax(options);