> Is he referring here to alternative protocols from http, or to the fact that behind the single http protocol are servers written in myriad languages and style

> Is he referring here to alternative protocols from http, or to the fact that behind the single http protocol are servers written in myriad languages and styles? My interpretation is that the design of TCP/IP (and maybe HTTP?) focuses on the behavior of the components from the perspective of how they communicate with one another, not how they behave internally. They follow the Robustness Principle: Be conservative in what you do, and liberal in what you accept from others. > What is a metasystem? Can you provide an example? Similarly, what are 2nd level architectures? It took me a long time to understand what this means. Basically, a metasystem is a blurring of the language and the code you write within that language. Smalltalk is an example of such a system because you can change the language itself from within the language and the environment. There are downsides to such a system, though, including the proliferation of many fragmented, inconsistent environments. To take a deliberately ridiculous example, let's imagine Ruby was a metasystem. You write some code in your rails app that allows a third method privacy mechanism beyond public, private, and protected. Or, that you decide you want multiple inheritance in ruby. That's powerful -- and dizzying for many people not accustomed to thinking about their languages at that level. So, what Alan is suggesting is that we erect "fences" of some kind to both allow this power in our languages but in a protected manner, so that we mitigate the risk of the fragmented world that could result. (Since you've essentially created a new "flavor" of ruby by changing its behavior.) There is a fantastic book on this topic called "The Art of the Metaobject Protocol" that I highly recommend. It guides you through building an object oriented language construct from within Common Lisp. I don't know what he means by 2nd-level architectures, nor what he's saying about assignments being meta-level change from functions.