Why is Preface to Lanting Collection called "the best running script in the world"? Please write down several reasons. (within 100 words)

The origin of "the best running script in the world" has two points. First of all, from the perspective of calligraphy itself, during the Jin Dynasty, due to the influence of gentry advocating Huang Lao and speaking freely, the calligraphy style gradually changed to pay more attention to brushwork and charm; From the characteristics of running script, it is more in line with the character of Wei and Jin Dynasties, so running script flourished most in the Jin Dynasty, which is also the highest achievement in the history of China calligraphy. There is only one copy of Preface to Lanting Collection in the world now, but its whole text is light and ethereal, natural and unrestrained, without any trace of carving, and it is natural. Moreover, what is most praised by later generations is that the same words are written in different ways, such as "Zhi", "Yi" and "Wei", each with its own changes. In particular, the word "zhi" has become more than 20 different brushstrokes, which is indeed the highest realm of Wang Xizhi's calligraphy art, and the Preface to Lanting is also a beautiful prose, which was passed down as Wang Xizhi's drunken work at that time. After waking up, Wang wrote more. But none of them have the charm of the first picture. Secondly, from a historical point of view, since the Southern Dynasties, Wang Xizhi's calligraphy has been highly praised by more and more people, and this Preface to the Lanting Pavilion has also risen with it, and Li Shimin, Emperor Taizong, liked this word best, and even let the ministers at that time learn it, making the book more prosperous. Unfortunately, the original was later buried in Zhaoling, and its whereabouts have been unknown since then. To sum up, running script is a font between regular script and cursive script. Wang Xizhi's true cursive script was praised by Yu Shuangjue (authentic script refers to the transitional regular script from Han Wei to Sui and Tang Dynasties, characterized by official script), praised by Emperor Taizong, and praised by later calligraphers as "the first running script", while Wang Xizhi himself was once rated as a grass saint and a calligrapher, and his peak work "Preface to Lanting" was called the world.