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Plan 9 - man page for utf (plan9 section 6)

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UTF(6)											   UTF(6)

       UTF, Unicode, ASCII, rune - character set and format

       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, pro-
       grams  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 them-
       selves 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 pre-
       sented 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 pro-
       cessing on ASCII graphic characters must convert from UTF to runes in order to work  prop-
       erly with non-ASCII input.  See rune(2).

       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 compat-
       ible 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 con-
       verted to rune hexadecimal 0080.

	      table of characters and descriptions, suitable for look(1).

       ascii(1), tcs(1), rune(2), keyboard(6), The Unicode Standard.

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