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 NAME     
 |  |  |  | UTF, Unicode, ASCII, rune – character set and format 
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 DESCRIPTION     
 |  |  |  | The Plan 9 character set and representation are based on the Unicode
    Standard and on the ISO multibyte UTF-8 encoding (Universal Character
    Set Transformation Format, 8 bits wide). The Unicode Standard
    represents its characters in 16 bits; UTF-8 represents such values
    in an 8-bit byte stream. Throughout this manual, UTF-8 is shortened
    to UTF. 
    
    
    In Plan 9, a rune is a 16-bit quantity representing a Unicode
    character. Internally, programs may store characters as runes.
    However, any external manifestation of textual information, in
    files or at the interface between programs, uses a machine-independent,
    byte-stream encoding called UTF. 
    
    
    UTF is designed so the 7-bit ASCII set (values hexadecimal 00
    to 7F), appear only as themselves in the encoding. Runes with
    values above 7F appear as sequences of two or more bytes with
    values only from 80 to FF. 
    
    
    The UTF encoding of the Unicode Standard is backward compatible
    with ASCII: programs presented only with ASCII work on Plan 9
    even if not written to deal with UTF, as do programs that deal
    with uninterpreted byte streams. However, programs that perform
    semantic processing on ASCII graphic characters must convert from
    UTF to runes in order to
    work properly with non-ASCII input. See rune(3). 
    
    
    Letting numbers be binary, a rune x is converted to a multibyte
    UTF sequence as follows: 
    
    
    01. x in [00000000.0bbbbbbb] → 0bbbbbbb 10. x in [00000bbb.bbbbbbbb] → 110bbbbb, 10bbbbbb
 11. x in [bbbbbbbb.bbbbbbbb] → 1110bbbb, 10bbbbbb, 10bbbbbb
 Conversion 01 provides a one-byte sequence that spans the ASCII
    character set in a compatible way. Conversions 10 and 11 represent
    higher-valued characters as sequences of two or three bytes with
    the high bit set. Plan 9 does not support the 4, 5, and 6 byte
    sequences proposed by X-Open. When there are multiple ways to
    encode a value, for
    example rune 0, the shortest encoding is used. 
    
    
    In the inverse mapping, any sequence except those described above
    is incorrect and is converted to rune hexadecimal 0080.
 
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 SEE ALSO     
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