Ci (tzu; simplified Chinese: 词; traditional Chinese: 詞; pinyin: cí; Wade–Giles: tz'u2, and, interchangeably –– to a point –– with 辭/辞) are a poetic form, a type of lyric poetry, done in the tradition of Classical Chinese poetry. Ci use a set of poetic meters derived from a base set of certain patterns, in fixed-rhythm, fixed-tone, and variable line-length formal types, or model examples: the rhythmic and tonal pattern of the ci are based upon certain, definitive musical song tunes. They are also known as Changduanju (長短句/长短句, "lines of irregular lengths") and Shiyu (詩餘/诗馀, "that which is beside poetry"). Typically the number of characters in each line and the arrangement of tones were determined by one of around 800 set patterns, each associated with a particular title, called cípái 詞牌. Originally they were written to be sung to a tune of that title, with set rhythm, rhyme, and tempo. Therefore, the title may have nothing to do with its contents, and it is common for several ci to share the same title, having little or nothing to do with the topics of those poems, but rather refers to their shared rhythmic and tonal patterns. Some ci would have a "subtitle" (or a commentary, sometimes as long as a paragraph) indicating the contents. Sometimes, for the sake of clarity, a ci is listed under its title plus its first line. Ci most often express feelings of desire, often in an adopted persona, but the greatest exponents of the form (such as Li Houzhu and Su Shi) used it to address a wide range of topics.