The Heart Sutra is a member of the Perfection of Wisdom (Prajnaparamita) class of Mahayana Buddhist literature; and along with the Diamond Sutra; is the most prominent representative of the genre. The Essence of Wisdom Sutra (Heart Sutra) is much shorter than the other Perfection of Wisdom sutras but it contains explicitly or implicitly the entire meaning of the longer Sutras. This sutra is classified by Edward Conze as belonging to the third of four periods in the development of the Perfection of Wisdom canon. Conze estimates the sutra's date of origin to be 350 CE. Recent scholarship is unable to verify any date earlier than the 7th century CE. The Chinese version is frequently chanted by the Chan (Zen/Seon/Thien) sects during ceremonies in China; Japan; Korea; and Vietnam respectively. It is also significant to the Shingon Buddhist school in Japan; whose founder Kukai wrote a commentary on it; and to the various Tibetan Buddhist schools; where it is studied extensively.