What is the "duality" in ancient poetry?

Duality, also known as duality, is a rhetorical device that arranges two phrases or sentences with equal words and the same structure or similarity in pairs.

For example, the water is bright and sunny, and the mountains are rainy and rainy, which have similar meanings and complement each other. Su Shi's first look at the lake after drinking rain)

Life is the song of the world, and death is the cry of the world.

Wildfire can't burn it out, but the spring breeze can revive it. (string pair-the same meaning, indicating coherence, progression, causality and other relations. (Bai Juyi's Farewell to Ancient Grass)