etudiant
China has had such a policy for at least 25 years to my certain knowledge. On 15th April 2020, the Taiwan Affairs Office, an organ of The State Council, repeated it in the form of an article by a leading Chinese nuclear strategy expert, Yang Chengjun, Check out casus belli number 4. It's in Chinese but I'm sure you'll cope. In my experience such articles are cleared at a high level.