"The additional content is rarely included in ordinary tours because of time constraints," Cao says.

"Generally, when it comes to the role of the Zhengda Guangming plaque, the explanation ends, without mentioning the drawbacks of the system. However, from the feedback I've received from tourists, they want further explanation," he adds.

Older tourists are interested in the role of the plaque, while children, he says, prefer to hear the stories about power struggles for the throne.

After graduating from the North China Institute of Science and Technology in 2008, Cao entered the tourism industry.

He started by entertaining tour groups to Beijing.

As a local, he felt it was the best of both worlds to make a living by promoting the charm of his hometown.

Through learning and preparing for the role, the job has enabled him to better understand the capital city, its culture and history.

"The Palace Museum is a place that most tourists will visit when they come to Beijing. It embodies the city's diverse culture in terms of history, architecture and aesthetics, and there are many interesting things to talk about," Cao says.

To ensure his guests get the best of what the city has to offer in their limited time, Cao has visited practically all the tourist attractions in Beijing, while attending training and communicating with scholars engaged in research of Beijing's history and culture.

He has incorporated what he has learned into his tours and shares the profound historical and cultural heritage of Beijing with his clients.

In 2017, Cao was chosen by the Beijing tourist guide association to be among a group of guides who would give in-depth tour explanations to enhance the cultural experiences of tourists to the city.

As his work experience grew, Cao also took outbound trips, including those to Germany, France and Italy.

"Compared with domestic trips, the biggest obstacle was the language," Cao says.

To improve his English proficiency, he memorized related English textbooks for tour guides and sought help from friends with strong foreign language abilities to practice speaking.