A clean room design ensures the new code is 100% original, and not a copy of the base code. That is why it is legally preferable, because it is easy to prove certain facts in court.

But fundamentally the problem is copyright, the copying of existing IP, not knowledge. grondo4 is completely correct that there is no legal framework that prevents learning from closed-source IP.

If such a framework existed, clean room design would not work. The initial spec-writers in a clean room design are reading the protected work.

>The initial spec-writers in a clean room design are reading the closed-source work.

Right. And they're only exposing elements presumably not covered by copyright to the developers writing the code. (Of course, this assumes they had legitimate access to the code in the first place.)

Clean room design isn't a requirement in the case of, say, writing a BIOS which may have been when this first came up. But it's a lot easier to defend against a copyright claim when it's documented that the people who wrote the code never saw the original.

Unlike with patents, independent creation isn't a copyright violation.

I don't understand what your point here is. The initial spec-writers learned from the original code. This is not illegal, we seem to be agreed on this point. grondo made the point that learning from code is not illegal.

What are you contesting?

My point was that, assuming access to the code was legit, and the information being passed from the spec-writers to the developers wasn't covered by copyright (basically APIs and the like), it's a much better defense against a copyright claim that any code written by the developers isn't a copyright violation given they never saw the original code.