var AllCheckbox = new Class ({
 
 initialize: function(mainCheckbox, children) {
    mainCheckbox.addEvent("change", function() {
        if (mainCheckbox.get("checked")) children.set("checked", "checked");
        else children.set("checked", "");
    });
    
    children.addEvent("change", function() {
        var checked = "checked";
        children.each(function(el) {
            if (!el.get("checked")) checked = "";
        });
        mainCheckbox.set("checked", checked);
    });
 }
 
});