How do Han Yu and Du Fu evaluate Zhang Xu's calligraphy?

Tang Hanyu praised in "Preface to Send a Noble Sage to a Master": "Emotion, embarrassment, sadness, happiness, resentment, longing, drunkenness, boredom and injustice, if moving in the heart, must be expressed in cursive script. Looking at things, we can see mountains and rivers, cliffs and canyons, birds, animals, insects, fish and flowers, the sun, the moon and stars, storms and fires, lightning and thunder, singing and dancing battles, and changes in heaven and earth. Congratulations, one is in one book, so the book of Xu is still as unpredictable as ghosts and gods, and it will eventually be praised by later generations. " This is a true portrayal of a real artist's dedication to art. Du Fu made such a wonderful description of Zhang Xu's calligraphy and people in Song of the Eight Immortals. He wrote: "Zhang Xu's three cups of grass, with his hat off, is like a cloud. Jiao Sui's five fights are outstanding and his eloquence is amazing. "