It is now possible to set the value of state properties to undefined using the set instance method.

It has been a long-standing shortcoming of the state properties mechanism that it has not been possible to "restore" properties back to an undefined state. It was always possible for the initial value for state properties to be undefined. However, once set to any value other than undefined, it was not possible to set their value back to undefined. The closest you could come was setting a property's value to null. This limitation has been fixed.

PREVIOUSLY

MyClass = Uize.subclass ();
MyClass.registerProperties ({_myProperty:'myProperty'});

var myClass = new MyClass;
alert (myClass.get ('myProperty'));    // alerts "undefined"

myClass.set ({myProperty:'solar'});
alert (myClass.get ('myProperty'));    // alerts "solar"

myClass.set ({myProperty:undefined});
alert (myClass.get ('myProperty'));    // alerts "solar"

With the new behavior, the last alert statement would display the text "undefined" in the alert dialog. That's because the set statement on the previous line would successfully set the property's value back to undefined.