> Yes, you can.  The mixin creates a new singleton class every time
> you do it, derived from the previous class.  My current thinking is
> that run-time roles work a little differently.  You get a singleton
> class for the object the first time you apply a property, so that each
> object's properties remain distinct.  However, subsequent properties
> re-use the existing singleton class, and do the same role-conflict
> checks at run time that "does" would do in the class definition
> at compile time.  Furthermore, the singleton class is not really
> derived from the original class, but just presents a different view
> of the same class, so that, from the viewpoint of the object, every
> role has the same standing, and run-time roles aren't privileged
> above compile-time roles, as they would be if the singleton class
> were really derived from the original class.  In a sense, the object
> thinks it's recomposing the original class, but it's slightly wrong.