The Yuan Dynasty was the heyday of Yuanqu. Generally speaking, Yuan Zaju and Sanqu are collectively called Yuanqu, and both of them use Beiqu as the singing form. Sanqu is the main body of literature in Yuan Dynasty. However, the achievements and influence of Yuan Zaju far exceeded that of Sanqu, so some people called Yuan Zaju "Yuan Qu" or "Yuan Qu".
Although there is a fixed framework, it is not rigid. Interlaced characters are allowed in the fixed frame, and sentences can be added to some qupai. In terms of rhyme, it is allowed to be flat and even, which is more flexible than quatrains and Song poems in metrical poems. Therefore, readers can find that two songs with the same "Qupai" sometimes have different words, which is the reason (the one with the least words in the same Qupai is the standard frame).