it's also called "xing". "If you are excited, you should first talk about other things to arouse the words you are chanting" (Zhu Xi's Biography of Poetry). That is to say, say other things first, and then say what you want to say. It is generally used at the beginning of a poem or section, and it is an artistic expression of "expressing feelings by borrowing things to attract others" based on sentences by using language factors. It has the functions of arousing feelings, creating the atmosphere of the work, coordinating rhythm, determining rhyme and step, and linking contextual relations. The use of improvisation can also make the language free to sing, and the writing is light and lively.