The other bit of that comment is also very insightful: "I would say that a system that allowed other metathings to be done in the ordinary course of programmin

The other bit of that comment is also very insightful: "I would say that a system that allowed other metathings to be done in the ordinary course of programming (like changing what inheritance means, or what is an instance) is a bad design. (I believe that systems should allow these things, but the design should be such that there are clear fences that have to be crossed when serious extensions are made.)"