As I said earlier, it is only somewhat similar to TLS-in-TLS blocking. I do not have exact articles right now, and it is not easy to google them, since almost all of them are in Chinese.

But here is for example, a proof of concept of a tool, that detects TLS-in-TLS: https://github.com/XTLS/Trojan-killer

It is incomplete and I do not know if it uses the same methods as Chinese censors, but it still proves the possibility.

If you still require more concrete proff, then, I will try to find an article in my free time and if I do, I would reply to your comment again after that (it is not going to be in the nearest future.