Where does "Don't boast that this place is divided into the world, but Xu Fei has to wear half makeup" come from?

From "Southern Dynasties" by Li Shangyin in the Tang Dynasty

Original:

The natural hazards are long and the natural hazards are long, and the king of Jinling should be radiant.

don't boast that this place is divided into the world, so Xu Fei has to wear half a makeup.

Translation:

Jinling is in a dangerous situation, with the Purple Mountain as its natural barrier and the vast Yangtze River as its natural barrier. Since ancient times, Jinling has always been a place where emperors can think for themselves, and its son of heaven should be radiant. Don't boast that according to Jinling, people can be divided into half of the world. In fact, they only got Xu Fei's half makeup.

Extended information:

Historical allusions of Xu Fei's half makeup

Xu Fei's half makeup said that the name of Xu Fei, the wife of Emperor Xiao Yi of Liang Yuan, was Zhao Pei. She was not very good-looking and had no appearance, so Yuan Di didn't like her very much after marriage, especially after she gave birth to two children, and she had to enter her room every two or three years.

In order to express her dissatisfaction and anger at the long-term cold reception, Xu Fei always puts on her makeup and waits in advance when she knows that Yuan Di is coming. It's just that her makeup is very special. What's special is that the tip of the nose is the vertical boundary. One face is made up with heavy makeup, and the other face is not made up, and it is always plain.

Xu Fei also euphemistically called this makeup method "half-face makeup", which was exclusively enjoyed by Yuan Di. When Yuan Di first saw Xu Fei wearing a half-face makeup, he dressed up to meet him. At first, he was surprised, and then he laughed and reminded, "Madam, you made a fool of yourself. Your makeup came out before it was finished. You don't have to be so impatient if you miss me."

Who knows that Xu Fei replied with a snort of sneer: "Husband, you only have one eye, so I just need to paint the makeup of one face. It is also a waste for you to make up both my faces. Anyway, you only have one eye, and you can't see my other face without makeup."

Yuan Di was very, very angry when he heard this. When he was a child, he lost one eye because of eye disease, so he was very, very afraid of being mentioned by others. Now, when he sees that Xu Fei actually reminds him that he has only one eye in person by painting half makeup, the meaning is clear enough. I am not very good-looking, but you are also blind.

Yuan Di couldn't help being furious and turned and slammed the door. After three transgressions, Yuan Di finally found another reason to force Xu Fei to commit suicide. Knowing that she was bound to die, Xu Fei committed suicide by jumping into a well.