In terms of content, popular things are the second kind. For example, the deeper academic content of Introduction to Oracle Bone Inscriptions is the first one. For example, the language study of offering sacrifices to Oracle Bone Inscriptions in Oracle bone inscriptions (these two terms are just an analogy, not necessarily one or the same).

In the past, the government was worried about the ideological poisoning of ordinary readers, but it was also a kind of research value for professional scholars, such as the research materials of Yuanyang Butterfly School and Jin Ping Mei.