Why do you say that crazy grass calligraphy "begins with Zhang and ends with Su"?

When it comes to weeds in China's calligraphy, we can't help but mention Zhang Xu and Huai Su. It can be said that "Zhang Dian Zuisu" founded and perfected the art of weeds. He has made immortal contributions to the development of China's calligraphy art. Zhang Xu is a bold and unrestrained drinker, and a drinking buddy of the great poet Li Bai. Li Bai has the reputation of "100 poems about fighting wine". Zhang Xu, like Li Bai, as long as he is drunk, his artistic thinking is extremely agile and his creation is extremely passionate. His handwriting is indulgent, like dragon and phoenix dance, with extraordinary momentum, like a whirlwind, billowing smoke and changing. His word is "Crazy Grass", also called "Zhang Dian". Coincidentally, Zhang Xu was followed by a monk named Huai Su, who was generous and informal, loved drinking and eating meat, and called himself a "crazy monk" and a "drunken monk". He was "crazy" and drunk as a fiddler. When he started to write, with the help of God, the pen galloped freely on the paper and the ink dripped freely on the paper. The written words are more indulgent than Zhang Xu's "Weeds", with more sonorous melody and more magnificent momentum. Their calligraphy is amazing to the world, so there is a saying that crazy grass calligraphy "begins with Zhang and becomes plain"