What is "tso-chan-i"

The Tso-chan-i (坐禅仪, Pinyin: Zuo-Chan-Yi, Principles of Zazen), is a short Chan Buddhist meditation manual attributed to a monk named Ch'ang-Iu Tsung-tse (c. 11th century) during the Northern Song dynasty (CE 960 - 1126) which exemplifies the practice of seated meditation which aims at "sudden" enlightenment. According to Peter Gregory it is the "earliest known work of its kind in the Zen tradition." The Tso-chan-i was later revised and expanded in 1202 by Yu Hsiang and this version was published together with Tsung-tse's monastic code ("Pure Regulations of the Zen Preserve"), the earliest extant Zen monastic code, which was widely circulated.