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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 repre‐
       sents its characters in 21 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 21-bit quantity representing a Unicode charac‐
       ter.  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

       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(2).

       Letting	numbers	 be  binary,  a rune x is converted to a multibyte UTF
       sequence as follows:

       01.   x in [000000.00000000.0bbbbbbb] → 0bbbbbbb
       10.   x in [000000.00000bbb.bbbbbbbb] → 110bbbbb, 10bbbbbb
       11.   x in [000000.bbbbbbbb.bbbbbbbb] → 1110bbbb, 10bbbbbb, 10bbbbbb
       100. x in [bbbbbb.bbbbbbbb.bbbbbbbb] →  1110bbbb,  10bbbbbb,  10bbbbbb,

       Conversion 01 provides a one-byte sequence that spans the ASCII charac‐
       ter set in a compatible way.  Conversions  10,  11  and	100  represent
       higher-valued  characters as sequences of two, three or four bytes with
       the high bit set.  Plan 9 does not support the 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 FFFD.

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

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

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