A Xuan paper pen is far away from the dragon and snake. What is Fang Qiu's square body?

In the Tang Dynasty, the secretary supervised the banquet for guests in the palace, and Li Bai wrote poems and cursive scripts on the table. Huai Su, a disciple of Master Xuanzang, was good at cursive writing and was asked to write in public. Huai Su dipped his pen in ink, absorbed in luck, and soon finished writing. He Zhangzhi praised that when the master wrote, he turned left and right, which was really a long snake. Therefore, there is a saying that "the Xuan paper pen is a dragon snake, and the four directions wave at Fang Qiu, and the cursive script refers to this cursive script".