What are the usages of introduction, inscription and postscript in the composition?

Postscript is written after a book or an article. Often used to explain the writing process, or evaluate the content, etc. Also known as postscript or postscript. In the Tang Dynasty, Han Yu's postscript to Kodou Book was called postscript. Ancient people often used book titles or afterwords. For example, after Ouyang Xiu's Shu Mei Yu Province Draft in Song Dynasty, Ceng Gong's Biography of Gong Zheng in Shu Wei and Wang Anshi's Collected Works of Li Shuwen, they all took the back of the book as the topic. Occasionally, titles like "After Reading" are used, such as Liu Zongyuan's Postscript on Reading Han Yu's Biography of Mao Ying in the Tang Dynasty. The so-called inscriptions and postscript in later generations are all postscript. The postscript is actually a preface listed at the back of the book (see preface), but it is slightly different from the preface. The difference lies in the postscript or postscript, the length is often smaller than the preface, the content is often not as comprehensive as the preface, and the scale of the system is also smaller than the preface.