The CNS 11643 character set (Chinese National Standard 11643), also officially known as the "Chinese Standard Interchange Code" (中文標準交換碼), is officially the standard character set of the Republic of China. (In practice, variants of Big5 are de facto standard.) CNS 11643 is a superset of ASCII designed to conform to ISO 2022.It contains 16 planes, so the maximum possible number of encodable characters is 16×94×94 = 141376. Planes 12 to 15 (35344 code points) are specifically designated for user-defined characters. Unlike CCCII, the encoding of variant characters in CNS 11643 is not related. EUC-TW is a representation of CNS 11643 in Extended Unix Code (EUC) form.