Within each rime subclass entries are ordered according to the thirty-six traditional initial onsets. The rime classes in "Menggu Ziyun" follow those given in "Gǔjīn Yùnhuì Jǔyào" 古今韻會舉要, a lexicographical compendium originally compiled by Huang Gongshao 黃公紹 (died 1297), and published in an abridged form by Xiong Zhong 熊忠 in 1297. However, the Chinese characters under each entry may be based on "Xīnkān Yùnlüè" 新刊韻略, a rime book compiled by Wang Wenyu 王文郁 during the late Jin dynasty (1115–1234) (the text is known from a manuscript copy of an edition published in 1229). The 36 initials are a traditional classification of initial onsets used in Chinese books dating back to the Tang dynasty (618–907), but by the Yuan dynasty they represented an idealized phonetic system that did not accurately reflect the Old Mandarin language that the 'Phags-pa script was designed to represent. The discrepancy between the theoretical and actual phonology of Yuan dynasty Chinese is indicated by certain peculiarities in the use of 'Phags-pa letters to represent the 36 initials in "Menggu Ziyun":   This use of variant forms of the letters "fa", "ha", "sha" and "ya" for different initials is not reflected in surviving inscriptions in the 'Phags-pa script, and is probably an attempt by Zhu Zongwen to artificially distinguish historical phonetic differences that were no longer valid in Yuan dynasty Old Mandarin. Works cited