The doctrine of Buddha-nature, as outlined in the "Ratnagotravibhāga" of Asanga, was also an important theory which became the basis for Tantric views. As explained by the Tantric commentator Lilavajra, this "intrinsic secret (behind) diverse manifestation" is the utmost secret and aim of Tantra. According to Alex Wayman this "Buddha embryo" ("tathāgatagarbha") is a "non-dual, self-originated Wisdom (jnana), an effortless fount of good qualities" that resides in the mindstream but is "obscured by discursive thought." This doctrine is often associated with the idea of the inherent or natural luminosity (Skt: "prakṛti-prabhāsvara-citta", T. "’od gsal gyi sems") or purity of the mind ("prakrti-parisuddha").