AutoCompleteExtenderCustomizedFunction

  var finalresult;
                //Customize the SetText function to create comma separated string from selected values
                Sys.Extended.UI.AutoCompleteBehavior.prototype._setText = function (item) {
                    var text = (item && item.firstChild) ? item.firstChild.nodeValue : null;
                    this._timer.set_enabled(false);
                    var element = this.get_element();
                    var control = element.control;
                    //Remove the first value from string which is basically user type for searching
                    if (typeof finalresult === 'undefined') {
                        element.value = "";
                    }
                    //Split the values
                    finalresult = element.value.trim().split(/,\s*/);
                    //Remove the first comma from string
                    finalresult = cleanArray(finalresult);
                    //Add the current existing value to finalresult variable
                    finalresult.push(text);
                    //Create Comma separated string from selected value
                    finalresult = finalresult.join(",");
                    //Assign the result to textbox control
                    if (control && control.set_text) {
                        control.set_text(finalresult);
                    } else {
                        element.value = finalresult;
                    }

                    $common.tryFireEvent(element, "change");

                    this.raiseItemSelected(new Sys.Extended.UI.AutoCompleteItemEventArgs(item, text, item ? item._value : null));

                    this._currentPrefix = this._currentCompletionWord();
                    this._hideCompletionList();
                };

                //Here we will Rewrite the _hideCompletionList function to keep the list shown all the time
                Sys.Extended.UI.AutoCompleteBehavior.prototype._hideCompletionList = function () {
                    var eventArgs = new Sys.CancelEventArgs();
                    this.raiseHiding(eventArgs);
                    if (eventArgs.get_cancel()) {
                        return;
                    }
                    //The hidePopup function is to close the CompletionList, so we need to
                    //  comment this line to ensure the CompletionList is visible.
                    //this.hidePopup();
                };

                function cleanArray(actual) {
                    var newArray = new Array();
                    for (var i = 0; i < actual.length; i++) {
                        if (actual[i]) {
                            newArray.push(actual[i]);
                        }
                    }
                    return newArray;
                }