When defining a class you use the userAlias. userAlias encompasses a number of different types, including xtypes. (when views and defined for xtypes are used it will automatically prefix with "widget.")
One of the benefits of using an event instead of a handler function is the fact that the this object will automatically be in the scope of the class you defined. In other words you don't have to do this.up() to find the class. You are already in the scope of the form.