[1] Zheng Lang himself passed the imperial examinations in the Jinshi class in 821, during the reign of Emperor Muzong, by which time Zheng Xunyu was deceased but Zheng Tan was already a prominent official—but his passage, as well as the passages of several other examinees related to prominent officials, including Pei Du's son Pei Zhuan (裴譔), Li Zongmin's son-in-law Su Chao (蘇巢), and Yang Yinshi (楊殷士) the brother of Yang Rushi (楊汝士), who was one of the lead examiners, were embroiled in controversy as the officials Duan Wenchang, Li Deyu, Yuan Zhen, and Li Shen, accused the examiners Yang Rushi and Qian Hui (錢徽) of being unfair in their decisions.
As a result, Emperor Muzong ordered a reexamination, while demoting Qian, Li Zongmin, and Yang Rushi, as well as the 10 examinees who passed based on perceived influence.
[2] As a result of this incident, Zheng Lang was not able to remain at Chang'an to start his official service, but instead served as a staff member of the military governor (jiedushi) Liu Gongchuo (柳公綽) at Shannan East Circuit (山南東道, headquartered in modern Xiangfan, Hubei).
[3][4] Zheng was eventually recalled to Chang'an to serve as You Shiyi (右拾遺), a low-level advisory official at the legislative bureau of government (中書省, Zhongshu Sheng).
[6] He was also made Zhongshu Shilang (中書侍郎), the deputy head of the examination bureau, as well as a senior scholar at Jixian Hall (集賢殿), in charge of editing the imperial history.