There are requirements of antithesis and adhesion in the seven-character rhythm poem, and there is no distinction between upper and lower queues, so it cannot be rhymed. However, as a epigraph, Yulouchun can have two queues, which can change rhyme in the lower queue. Words are not as strict as poems, but there are strict hierarchical restrictions, which are not as strict as poems.
For example, there is a song "Flower Collection" by Niu Qiao:
In spring, you walk into a horizontal pond and shake shallow waves. The flowers in the small garden are empty and melancholy. Who believes this is a madman and hates Cui Chou's pillow? Xiaoyu speaks at the window. Red tears dripped through the gold thread. The wild goose will not return to Lang, but will be woven into a brocade seal.
This word format, each song is two pieces. Each film consists of four seven-character sentences. Use rhyme, and the next film will be rhymed. If the next one doesn't change its rhyme, it will be like a seven-character poem. In Wen Feiqing's poetry collection, there is a "Song of Spring Dawn":
In Ru Yan's long letter home, both of them brushed tobacco. Oil wall car light golden calf fat, tassel account Xiao Chun chicken newspaper. The charming bird in the cage is still warm and sleeping, and the fallen flowers outside the curtain have not been swept. A rotten peach tree approached the pool, as if cherishing the beautiful scenery in the mirror.
This poem was compiled into "Caotang Poetry" by people in the early years of the Southern Song Dynasty. It is divided into two parts, including eight sentences, and renamed as "Yulouchun". So it is considered a word.
Thus, in fact, the difference between Yulouchun and Seven-character Rhyme is very subtle. The so-called poetry has never been separated since ancient times.