 However, regardless of the chronological difficulties, major developments of poetry during the Six Dynasties include formalizing the distinction between the "Jian'an" era regular "yuefu" and the "shi" style poetry, further development of the "fu", theoretical work on technique, and the preservation of both Six Dynasties and earlier poetry by collecting and publishing many of the pieces which survive today into various anthologies consisting all or in part of poetry.The Six Dynasties poetic period formed an important link between the folk-ballad ("yuefu") style prominent in the poetry of the Han dynasty and the following revival and experimentation with the older forms during the Tang dynasty.Even before the formal end of the Han Dynasty the poetic developments typical of that era had begun to yield to the Jian'an style, just as the political power of Han yielded more and more to that of the rising power of various regional hegemons, including Cao Cao and the Cao family.