The idiom is also explained as "Dragon is the guest of honor". Records of the Historian: "The Yellow Emperor collected bronze from the first mountain and cast a tripod at the foot of Jingshan Mountain. The tripod has been set, and a dragon hangs down to meet the Yellow Emperor. The Yellow Emperor rode on, and there were more than 70 people from the harem of ministers, and the dragon was on it. " Later, he used "Long Yu Shang Bin" as the taboo of the emperor's death. It means that Lapras ascended to heaven and was the guest of the Emperor of Heaven.
The idiom comes from the Book of Records of the Historian: "The Yellow Emperor picked bronze from the first mountain and cast a tripod at the foot of Jingshan Mountain. The tripod has been set, and a dragon hangs down to meet the Yellow Emperor. The Yellow Emperor rode on, and there were more than 70 people from the harem of ministers, and the dragon was on it. "