This kind of article belongs to expository or argumentative according to the content, and it is expository that explains the writing purpose, style and content. Comments on the author's works or explanations are argumentative. The prefaces I have learned are: Introduction to Scream, Preface to Rural Survey, Postscript to Southern Guide, Biography of Lingguan, etc.
In ancient times, there was also a kind of preface, which was a farewell message, called "preface of giving words". Its content was mostly praise, praise or encouragement to the relatives and friends given, and it was a farewell message. For example, Song Lian's Preface to Send Ma Sheng to Dongyang is a gift preface written by the author to 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. Such as Peacock Flying Southeast by Han Yuefu, Pipa Trip by Bai Juyi and Yangzhou Slow by Jiang Kui.
Extending data sequence styles is one aspect of writing styles. There are a few people who make a "preface" at every meeting because they are emotional. Because they haven't read the manuscript carefully, they have to list trivial matters or spread anecdotes at will. Results Preface and text are often irrelevant, and order equals disorder. This is really a bad style of writing.
Foreword is mostly a discussion between narration and discussion. Inclined to narrative, with the characteristics of prose; Tending to discuss, with the characteristics of the paper. Prose or thesis should have written content. Prose should be good at the richness of materials and the diversity of writing, and the paper should win with the profundity of arguments and the breakthrough of analysis. In various applied styles, the preface has important literary or historical value.
References:
Baidu encyclopedia-preface