“Mr. Cài” (Cài shì 蔡氏) is the catalog-meta authorial attribution of Huángdì yīnfú jīng zhù 黃帝陰符經註 (DZ 118); the name refers to Zhū Xī 朱熹’s (1130–1200) student Cài Yuándǐng 蔡元定 (1135–1198), but the commentary itself is actually Zhū Xī’s own exegesis of the Yīnfú jīng, transmitted via his student-circle and published under the student’s name (cf. Reiter in Schipper & Verellen 2004, 2:696). The text is identical with the first portion of [[KR5a0124|DZ 124 Huángdì yīnfú jīng zhùjiě]] 1a–8a. The Zhū Xī / Cài Yuándǐng authorship combination is an important witness to Neo-Confucian engagement with the Yīnfú jīng within the Daoist-canon tradition. No independent biographical note is warranted for “Cài shì” since the attribution-name does not denote a distinct historical person beyond the Zhū–Cài Neo-Confucian master-disciple pair.