When I wrote that I was thinking of rewording it, but I thought people would get it just the same. I meant that the clienet would stand alone to power whatever mod you put into it. For instance, if you got this fabled engine, you would not be able to play HL 1 player unless you owned it. You could mod it by loading on CounterStrike and bots. That's what I meant.
HOWEVER, since the system of which I speak isn't real and was only a mistake in my reading up on STEAM 2.0, there's no more need to worry about that aspect of this discussion

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EDIT: I apologize for any misuse of lingo. Namely, I think I misused th word "engine."
~Neszis~