Please answer the following question: I know that the answer to the question "What did Buddha improve?" is in "Meditation was an aspect of the practice of the yogis in the centuries preceding the Buddha. The Buddha built upon the yogis' concern with introspection and developed their meditative techniques, but rejected their theories of liberation. In Buddhism, mindfulness and clear awareness are to be developed at all times; in pre-Buddhist yogic practices there is no such injunction. A yogi in the Brahmanical tradition is not to practice while defecating, for example, while a Buddhist monastic should do so.". Can you tell me what it is?
A:
built upon the yogis' concern with introspection and developed their meditative techniques