// cross browser function for registering event handlers
var registerEventListener = null;
if (typeof addEvent != 'undefined') {
    // use Dean Edwards' function if available
    registerEventListener = function (elem, event, func) {
        addEvent(elem, event, func);
        return true;
    }
} else if (window.addEventListener) {
    registerEventListener = function (elem, event, func) {
        elem.addEventListener(event, func, false);
        return true;
    }
} else if (window.attachEvent) {
    registerEventListener = function (elem, event, func) {
        var result = elem.attachEvent("on"+event, func);
        return result;
    }
} else {
    registerEventListener = function (elem, event, func) {
        return false;
    }
}
// cross browser function for unregistering event handlers
var unRegisterEventListener = null;
if (typeof removeEvent != 'undefined') {
    // use Dean Edwards' function if available
    unRegisterEventListener = function (elem, event, func) {
        removeEvent(element, event, func);
        return true;
    }
} else if (window.removeEventListener) {
    unRegisterEventListener = function (elem, event, func) {
        elem.removeEventListener(event, func, false);
        return true;
    }
} else if (window.detachEvent) {
    unRegisterEventListener = function (elem, event, func) {
        var result = elem.detachEvent("on"+event, func);
        return result;
    }
} else {
    unRegisterEventListener = function (elem, event, func) {
        return false;
    }
}