According to Shan Hai Jing, every time the Queen Mother of the West travels, she always asks a Qingluan to inform her first. Later generations used "qingluan" and "bluebird" to refer to the messenger who delivered the message. Song Zhao Ganoderma lucidum's poem "Dead Hua Lian" says: "Forget about eating and sleeping. Look at qingluan, not fish and geese. " Qing Nalanxingde's "Shanghai Tang Zhong Yuan beyond the Great Wall" says: "The blue sky and the sea of clouds are beautiful."
Therefore, Qingluan books generally refer to letters from people missed by relatives and friends.