In ancient times, what did the style of preface mean?

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, such as Lu Xun's preface; The preface written by others is called "preface", which introduces and comments on the ideological content and artistic characteristics of the book. For example, 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 narration and lyricism, while Sun Yat-sen's Preface integrates narration, lyricism and argumentation. 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.