Kan'on, a Sino-Japanese kanji pronunciation layer; based mainly on the Chinese pronunciation in use in the areas around Chang'an (around modern-day Xi'an) and Henan, as imported into Japanese in the Nara period and the early Heian period in Japanese history, and roughly from the late Tang Dynasty through the early Song Dynasty in Chinese history. The predominant layer used in Japanese today, as opposed to the other layers which are associated with restricted sets of words (Buddhism, etc.).