gistfile1.js

// The idea behind ATTRS, is that Base will take care of 
// setting up the attributes defined in ATTRS for each
// subclass. So, you don't need to do anything special
// for Class2's ATTRS definition.

// Changing Class2 to this should take care of it.

var Class2 = function(config) {
    Class2.superclass.constructor.apply(this, arguments);
};

Y.mix(Class2, {
   NAME: "class2",
   ATTRS: {
      // Any new attributes Class2 introduces
      width: {...},
      height: {...}
   }
});

Y.extend(Class2, Class1, {
   // Prototype properties
});