What does the "subset of classics and history" mean respectively, and how to distinguish it?

Jing: Jing Shu refers to Confucian classics; History: history books, that is, official history; Zi: Hundreds of works in the pre-Qin period, religion; Collection: Collection of poems. Generally refers to ancient Chinese classics. Source: The Book of the New Tang Dynasty: "The two capitals each have four books, followed by A, B, C and D, and they are listed in the four databases of the subset of classics and history." Example: just say a word from my sister, no matter ~, everyone will continue to be numb in turn. The seventy-eighth chapter of Jing Hua Yuan by Li Ruzhen in Qing Dynasty "A subset of classics and history" is the four major categories of ancient books in China according to their contents. Some large-scale ancient books series often include four books and are named after them, such as Si Ku Quan Shu, Si Bu Series, Si Bu Yao, etc., which shows the important significance of four categories to ancient books.