Writing style means expressing knowledge, which was initiated by Zheng Xuan. Zheng Xuanzhi's poem respects Mao Zhuan. If "Biography of Mao" is obscure, he will write down his views, mark them and become "notes". After Zheng Xuan's Annotations on Mao Poetry, there appeared countless works explaining classics through annotations. In the Qing Dynasty alone, there were Hu Yongyun's Notes on Mao Poetry, Zhou Guan's Notes, Li Ji's Notes, Yu Yue's Notes on Li Ji and Liu's Notes on Ram.