Why did Zhang Zeduan name the painting he painted "Along the River During the Qingming Festival"?

"Along the River During Qingming Festival" depicts the conditions of Tokyo (now Kaifeng, Henan Province), the capital of the Northern Song Dynasty, mainly the natural scenery and prosperity of Bianjing and both sides of the Bianhe River.

Going up the river during the Qingming Festival was a folk custom at that time. Like today's festival gatherings, people used it to participate in business activities. The whole picture is roughly divided into three parts: spring scenery in the suburbs of Bianjing, scenes on the Bianhe River, and markets in the city.