What other ancient poetic ideology did Yan Yu put forward in Cang Shi Lang Hua?

In Cang Shi Lang Dialect, Yan Yu also put forward an ideology of imitating ancient poetry. He established the core of "learning from the past" in poetic theory, and also determined that the object of study and imitation was the works of poets in Han, Wei, Jin and Tang Dynasties. Regarding the aesthetic characteristics of poetry, Yan Yu put forward the theory of "different materials" and "different interests".