What are the artistic features of Sun's calligraphy?

Sun, whose real name is unknown. Activities in Wuhou period. Zeng Guan led government clerks to join the army. Preface to Book Spectrum is his masterpiece. This book has been hung for three years (687) and has more than 3,500 words. It is not only an outstanding calligraphy theory article, which occupies an important position in the history of calligraphy, but also an excellent calligraphy work, which represents the highest level of cursive script in the early Tang Dynasty and is considered as the direct descendant of the cursive script of the two kings. Zhang Huaiguan said that he was "the two kings of the cursive charter, who tried to use a pen and just broke it". Some people also criticized him for "being quick will hurt your health" and "being stereotyped and centralized", which is shorter than no change.