addIframeMask: function(c) {
                if (dnn.dom.browser.isType("ie") && (c.previousSibling == null || c.previousSibling.nodeName.toLowerCase() != "iframe")) {
                    var a = document.createElement("iframe");
                    c.parentNode.insertBefore(a, c);
                    var b = c.getBoundingClientRect();
                    a.style.position = "absolute";
                    a.style.left = c.offsetLeft + "px";
                    a.style.top = c.offsetTop + "px";
                    a.style.width = b.width + "px";
                    a.style.height = b.height + "px";
                    a.style.opacity = "0";
                    a.style.zIndex = "-1";
                    return a
                }
                return null
            },