true nature of phenomena, also defined as "seeing things as they truly are" (yathābhūtaṃ darśanam). A unique feature of classical Buddhism is its understanding of all phenomena (dhammas) as being empty of a self.Paul Williams (2008). Mahayana Buddhism: The Doctrinal Foundations. Routledge. pp. 68–69. . Later developments in Buddhist traditions led to innovations in yoga practice. The conservative Theravada school developed new ideas on meditation and yoga in its later works, the most influential of which is the Visuddhimagga. Mahayana meditation teachings may be seen in the Yogācārabhūmi-Śāstra, compiled c. 4th century. Mahayana also developed and adopted yoga methods such as the use of mantras and dharani, pure land practices aiming at rebirth in a pure land or buddhafield, and visualization. Chinese Buddhism developed the Chan practice of Koan introspection and Hua Tou. Tantric Buddhism developed and adopted tantric methods which are the basis of the Tibetan Buddhist yoga systems, including deity yoga, guru yoga, the six yogas of Naropa, Kalacakra, Mahamudra and Dzogchen. Classical yoga What is often referred to as classical yoga, ashtanga yoga, or rāja yoga is primarily the yoga outlined in the dualistic Yoga Sutras of Patanjali. The origins of classical yoga are unclear, although early discussions of the term appear in the Upanishads. Rāja yoga (yoga of kings) originally denoted the ultimate goal of yoga; samadhi, but was popularised by Vivekananda as a common name for ashtanga yoga, the eight limbs attain samadhi as described in the Yoga Sutras. Yoga philosophy came to be regarded as a distinct orthodox school (darsanas) of Hinduism in the second half of the first millennium CE. Classical yoga incorporates epistemology, metaphysics, ethical practices, systematic exercises and self-development for body, mind and spirit. Its epistemology (pramana) and metaphysics are similar to the Sāṅkhya school. The Classical yoga's metaphysics, like Sāṅkhya's, primarily posits two distinct realities: prakriti (nature, the eternal and active unconscious source of the material world composed of three Gunas) and puruṣa (consciousness), the plural consciousnesses which are the intelligent principles of the world. Moksha (liberation) results from the isolation (kaivalya) of puruṣa from prakirti, and is achieved through meditation, stilling one's thought waves (citta vritti) and resting in pure awareness of puruṣa. Unlike Sāṅkhya, which takes a non-theistic approach, the yoga school of Hinduism accepts a "personal, yet essentially inactive, deity" or "personal god" (Ishvara). In Advaita Vedanta Vedanta is a varied tradition, with a number of sub-schools