In the classification number Z42:
Z stands for comprehensive books.
4 represents a collection of essays.
2 stands for China
Generally, this is enough, and there is no need to subdivide it.
If it needs to be subdivided, it should be divided according to China time in the subdivision table of China Library Classification.
Song belongs to Sui Dynasty, from Tang Dynasty to early Qing Dynasty, and the compound semicolon is 4.
Then the classification number is Z424.