In order to facilitate writing, after a long process of convention, especially in the period of the transformation from seal script to official script, the popular cursive script has gradually increased and the writing method has gradually unified. After the process of quantitative change to qualitative change, a cursive script with statutes was finally produced, that is, Cao Zhang, which further developed into today's cursive script. In a narrow sense, cursive script refers to Cao Zhang and today's grass.