The CNS 11643character set, also officially known as the Chinese Standard Interchange Code or CSIC, is officially the standard character set of the Republic of China. In practice, variants of the related Big5 character set are de facto standard. CNS 11643 is designed to conform to ISO 2022. It contains 16 planes, so the maximum possible number of encodable characters is 16×94×94 = 141376. Planes 1 through 7 are defined by the standard; since 2007, planes 10 through 15 have also been defined by the standard. Prior to this, planes 12 to 15 were specifically designated for user-defined characters. Unlike CCCII, the encoding of variant characters in CNS 11643 is not related. EUC-TW is a encoded representation of CNS 11643 and ASCII in Extended Unix Code form. Other encodings capable of representing certain CSIC planes include ISO-2022-CN and ISO-2022-CN-EXT.
History
The first edition of the standard was published in 1986, and included planes 1 and 2, deriving from levels 1 and 2 of Big5, with some re-ordering due to corrected stroke counts, two duplicate characters being omitted, and the addition of 213 classicalradicals. Extensions to the standard were subsequently published in 1988 and 1990. When the Unicode CJK Unified Ideographs set was being compiled for Unicode 1.1, the national bodies submitted character sets to the CJK Joint Research Group for inclusion. The version of CNS 11643 submitted included the plane 14 extension, in addition to further desired characters appended to plane 14. In the second edition of the standard, published in 1992, a much larger collection of hanzi was defined across seven planes. A subset of the 1988 plane 14 extension, including the 6148 code points 01-01 through 66-38, became plane 3. The plane 15 extension was not included, although 338 of its characters were included amongst planes 4 through 7. The third edition of the standard, published in 2007, added the Euro sign, ideographic zero, kana and extensions to the existing bopomofo and Roman alphabet support to plane 1. It introduced planes 10 through 14, containing additional hanzi, and incorporated the existing plane 15 extension into the standard itself. It also added 128 further hanzi to plane 3, starting at code point 68-40. , there are several thousand CNS 11643 characters with no corresponding Unicode character, mostly in planes 10 through 14; these are mapped to the Unicode Supplementary Private Use Area.
Relationship to Big5
Levels 1 and 2 of the Big5 encoding correspond mostly to CNS 11643 planes 1 and 2, respectively, with occasional differences in order. They can be mapped using a list of ranges. The Big5-2003 variant of Big5 is defined as a partial encoding of CNS 11643.
