1. Yangchunbaixue: a metaphor for high and uncommon literary art.

Source: Warring States Chu Song Yu "to the king of Chu asked": "Guests have songs in Ying, the beginning of its said: "under the Li", "Ba Ren", the country belongs to and thousands of people. ...... Its for 'Yangchun', 'Baixue', the country belongs to and and those who are but a few dozen."

Translation: A guest came to our Ying capital to sing. He began by singing the very popular "Xia Li" and "Ba Ren", and there were thousands of people in the city who sang along with him. Then he sang the popular "Yanga" and "Allium dew", and the city sang with him much less than at the beginning, but there were still several hundred people. Later he sang the more difficult ones? Yangchun and Baixue, there were only a few dozen people in the city who sang with him.

2. Lower Li Ba Ren: originally refers to a kind of popular folk song in Chu during the Warring States period, now used as a metaphor for popular literature and art.

Source: the warring states chu song yu "to the king of chu asked": "the guest has a song in ying, the beginning of which said: "the lower barren", the state belongs to and and thousands of people."

Translation: A guest came to our Ying capital to sing. He began to sing the very popular "Xia Li" and "Ba Ren", and there were thousands of people in the city who sang along with him.

Yangchunbaixue and XiaLiBaRen are antonyms of each other.

Expanded Information

Allusion

Song Yu was an opinionated official in the late Warring States period of Chu, who never agreed with others' ideas. When the king of Chu heard others say something bad about him, he brought Song Yu to him and asked, "Are you doing something wrong? Why are so many people dissatisfied with you?" Song Yu replied, "Let me tell you something first! There was a singer who sang in the capital.

Starting out with the most popular folk song in Chu, 'The Lower Mainland', at which point several thousand of the onlookers sang along. Then he sang the more sophisticated "Yang'a Allium Dew," and only a few hundred people sang along. When he sang the more elegant song "Yangchunbaixue", there were only a few dozen people left singing along.

Finally, he sang a song of the highest order with a special harmony of the five tones and six rhythms. There were only a few people who could sing along. It can be seen that the more advanced the song is, the fewer people can sing along!" Then Song Yu added, "It is the same among the literati. Those outstanding figures with lofty aspirations and noble behavior, of course the general public will not understand, and this is exactly what happened in my case!" The king of Chu heard these words of Song Yu and found them very reasonable. Then he did not pursue further.

The idiom of "Yangchunbaixue" and "Xiali Baren" is derived from this. The idiom "Yangchunbaixue" was later used to represent elegant literature, while "Xiali Banren" represented literature that was easy to understand.

References:

Baidu Wikipedia - Lower Li Ba Ren

Baidu Wikipedia - Lower Li Ba Ren

Baidu Wikipedia - Literature and Art. The Lower Mainland