Now to create a proxy you need to subclass ProtoObject and not nil.

This was changed years ago to avoid some issues. An example of issue that existed: when you subclass nil, as��

#doesNotUnderstand: is not implemented by default on your proxy, any proxy created receiving a message would crash the VM if you had not overridded #doesNotUnderstand:. Another example is that when you iterate over memory using #nextObject, if the proxy does not answer it you can end with severe VM crashes. In these examples I am talking about the expected VM behavior and not about bugs.

So basically the purpose of ProtoObject was to limit the number of VM crashes when playing with proxies / ProtoObjects, instead having a default behavior for several messages such as #doesNotUnderstand: or nextObject.��

Note that the IDE support for ProtoObject is limited as ProtoObject API is very restricted so it does not have methods such as #inspect, ... That's also on purpose because Proxies may not implement introspection methods.