function cb(){
                var me = this,
                    // bogus response object
                    r = {responseText : '',
                         responseXML : null,
                         argument : o.argument},
                    doc,
                    firstChild;

                try{
                    doc = frame.contentWindow.document || frame.contentDocument || WINDOW.frames[id].document;
                    if(doc){
                        if(doc.body){
                            if(/textarea/i.test((firstChild = doc.body.firstChild || {}).tagName)){ // json response wrapped in textarea
                                r.responseText = firstChild.value;
                            }else{
                                r.responseText = doc.body.innerHTML;
                            }
                        }
                        //in IE the document may still have a body even if returns XML.
                        r.responseXML = doc.XMLDocument || doc;
                    }
                }
                catch(e) {}

                Ext.EventManager.removeListener(frame, LOAD, cb, me);

                me.fireEvent(REQUESTCOMPLETE, me, r, o);

                function runCallback(fn, scope, args){
                    if(Ext.isFunction(fn)){
                        fn.apply(scope, args);
                    }
                }

                runCallback(o.success, o.scope, [r, o]);
                runCallback(o.callback, o.scope, [o, true, r]);

                if(!me.debugUploads){
                    setTimeout(function(){Ext.removeNode(frame);}, 100);
                }
            }
Aborts any outstanding request.
@param {Number} transactionId (Optional) defaults to the last transaction