Poetic songs were developed from the officially collected folk ballads and songs of the Han, Wei and Six Dynasties. They are characterized by great length, bold expression of feeling, diverse sentence patterns and laxity of the requirements of metrical forms. They followed the classic forms of five characters to a line, seven characters to a line and a mixed pattern in a flexible manner. This genre was established by Southern Dynasty poet Bao Zhao who drew inspiration from folk songs. Tang Dynasty poets Li Bai and Bai Juyi also wrote poems in such style.
Ge (歌 singing) refers to long chanting and offers lines of varying lengths unrestrained by metrical rules; Xing (行 smooth-flowing) refers to chanting that freely and fluently accelerates or decelerates. If both Ge and Xing are involved, it is termed gexing (歌行 free and flowing chanting or poetic song). (Xu Shizeng: Interpreting the Different Types of Poetry)
Gexing refers to chanting poetry in a free, flowing and unrestrained manner, as opposed to adhering meticulously to the standard guidelines of classic poetry. Thus, the sentence patterns, phrasing, metrical schemes and tonal effects of these two types of poetry end up being different to some extent. (Wu Ne: Collected Prefaces for Different Types of Writing)