What is a preface and postscript? (clear explanation)

Preface, also known as "preface", "preface" and "introduction", is an article placed before the text of a work. The author's own writing is called "preface", which mostly explains the purpose and process of writing a book; The preface written by others is called "preface", which introduces and comments on the ideological content and artistic characteristics of the book. The former is Lu Xun's Preface, and the latter is Mao Zedong's Preface. Language expression is flexible, which can be based on one expression or a combination of multiple expressions. For example, Wen Tianxiang's Preface is a combination of narrative and lyric, while Sun Yat-sen's A Brief Introduction to Seventy-two Martyrs in Huanghuagang is a combination of narrative, lyric and argumentative. In ancient times, there was another kind of preface, that is, farewell words, which was called "preface of giving words" Most of the content is words that praise, emphasize or encourage relatives and friends. For example, Song Lian's "Preface to seeing Ma Sheng off to Yang" is the preface written by the author to the younger generation in his hometown. There is also a preface written in front of a poem, called "preface to poetry", which is more about telling the content of the story or the source of the poem. For example, Peacock Flying Southeast by Han Yuefu, Pipa Trip by Bai Juyi and Yangzhou Slow by Jiang Kui are all in order. Postscript is also called postscript, which is used to supplement postscript and postscript. It's usually the author's. Thank you. Feelings or something.