The "Cao" may also be from Cáoxī (曹溪), the "mountain-name" of Huineng, the Sixth Ancestor of Chan, as Caoshan was of little importance unlike his contemporary and fellow Dharma-heir, Yunju Daoying.
Sayings to the effect that Shitou and Mazu were the two great masters of their day date from decades after their respective deaths.
Under Hongzhi and Zhengzie Qingliao, the Caodong school was revived and became one of the major traditions of Song dynasty Chan.
[1] These Song era teachers taught a practiced termed "silent illumination" or "serene reflection" (Ch: 默照禅) which relied on the doctrine of inherent enlightenment and buddha-nature.
[7] In 1227 Dōgen Zenji, a former Tendai student, studied Caodong Buddhism under Tiantong Rujing, and returned to Japan to establish the Sōtō sect.
It was brought to the north Vietnam in the late of 17th century by Thiền master Thông Giác Thủy Nguyệt (通覺水月, 1637-1704), a disciple of Yiju Zhijiao (一句智教).
Chan master Zhijiao is the 4th generation after Zhanran Yuancheng (湛然圓澄, 1561-1626) - one of Caodong school's famous revivers in late Ming period.