As pointed out, this question will be relevant only if you are be referring to the Ci 詞 form, prevalent in the Song 宋 dynasty, which is traditionally sung by courtesans. Strictly speaking, this will not be 'new material'; nonetheless, modern songs do use the form occasionally. An example will be the Nian4 Nu2 Jiao1 by Su1 Shi4:
The format for such literary form are usually given by the Ci2pu3 詞譜 or lyric score, which defines the number of letters in each phrase, the intonation of each letter, and where the rhyme should land. Nian4 Nu2 Jiao1 is the name of the song, or Ci2 Pai2 詞牌. Different songs will usually demand different phrasing, rhyming and intonation strategies, just as we do in song writing today. So, the Nian4 Nu2 Jiao1 format above, as given by the Bai2xiang1 ci2pu3《白香詞譜》will go like this:
Each symbol corresponds to a letter. ▲ indicates where the rhyme lands while ●○⊙ indicates the intonation. Note the similarity in phrasing to the song quoted above.
The Ci2 is also known as the 長短句, or long-short verse, due to the varying number of letters in each phrase, as contrasted with the Shi1 詩, which is usually of uniform meter (such as the pentametric poem or 五言詩).