function UserDataStorage(maxage) {
 // Create a document element and install the special userData
 // behavior on it so it gets save() and load() methods.
 var memory = document.createElement("div"); // Create an element
 memory.style.display = "none"; // Never display it
 memory.style.behavior = "url('#default#userData')"; // Attach magic behavior
 document.body.appendChild(memory); // Add to the document
 // If maxage is specified, expire the userData in maxage seconds
 if (maxage) {
 var now = new Date().getTime(); // The current time
 var expires = now + maxage * 1000; // maxage seconds from now
 memory.expires = new Date(expires).toUTCString();
 }
 // Initialize memory by loading saved values.
 // The argument is arbitrary, but must also be passed to save()
 memory.load("UserDataStorage"); // Load any stored data
 this.getItem = function(key) { // Retrieve saved values from attributes
 return memory.getAttribute(key) || null;
 };
 this.setItem = function(key, value) {
 memory.setAttribute(key,value); // Store values as attributes
 memory.save("UserDataStorage"); // Save state after any change
 };
 this.removeItem = function(key) {
 memory.removeAttribute(key); // Remove stored value attribute
 memory.save("UserDataStorage"); // Save new state
 };
}