The emperor is dead. What does Zhen Xuan mean by pulling the tape?

In the TV series The Queen of the Palace, the emperor pulled the tape before he died because he wanted to kill Zhen Xuan.

Before the emperor died, Zhen Xuan told him all the truth, so that he could die clearly and vent his resentment. Including his affair with King Guo Jun, the life experience of twins and Meizhuang's daughter, made the emperor very angry.

The emperor said indignantly: after I want to kill you, I reached out to broach the yellow belt in front of the bed, obviously I have moved my heart.

In some ancient rules, there is a saying called "If the yellow belt is broken, you will be suspected of dying. Once this yellow belt is broken, everyone present will die. At that time, Zhen Xuan spent all his money, and Zhen Xuan was the only one in the whole bedroom, so Zhen Xuan told the truth clearly.

In the end, the emperor didn't break his belt:

However, the emperor in the play pulled the yellow belt for a long time, and the yellow belt didn't break. The emperor also took off his strength and lay in bed, dying unsatisfied.

When the emperor went to pull the yellow ribbon, Zhen Xuan watched and didn't stop him. I should know that the emperor is weak now, and with his strength, he can't pull the yellow belt, so he is happy to watch him die coldly.