There are many differences in the number of words in a word when you fill in words according to the length and change of musical tune. According to the number of words, it can be generally divided into three categories: poem, middle tune and long tune. Mao Xianshu, a Qing Dynasty poet, said in "The Explanation of Ci-writing": "A poem within fifty-eight characters is a minor tune, a tune from fifty-eight to ninety is a middle tune, and a tune beyond ninety-one characters is a long tune." This division is too absolute. For example, the epigraph of "The Lady" has 58 characters and 6 characters, so it can't be hard to divide it into a poem or a middle tone.