locale/FreeBSD/utf8.5

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  31 .\"     @(#)utf2.4      8.1 (Berkeley) 6/4/93
  32 .\" $FreeBSD: src/lib/libc/locale/utf8.5,v 1.7 2007/01/09 00:28:01 imp Exp $
  33 .\"
  34 .Dd April 7, 2004
  35 .Dt UTF8 5
  36 .Os
  37 .Sh NAME
  38 .Nm utf8
  39 .Nd "UTF-8, a transformation format of ISO 10646"
  40 .Sh SYNOPSIS
  41 .Nm ENCODING
  42 .Qq UTF-8
  43 .Sh DESCRIPTION
  44 The
  45 .Nm UTF-8
  46 encoding represents UCS-4 characters as a sequence of octets, using
  47 between 1 and 6 for each character.
  48 It is backwards compatible with
  49 .Tn ASCII ,
  50 so 0x00-0x7f refer to the
  51 .Tn ASCII
  52 character set.
  53 The multibyte encoding of
  54 .No non- Ns Tn ASCII
  55 characters
  56 consist entirely of bytes whose high order bit is set.
  57 The actual
  58 encoding is represented by the following table:
  59 .Bd -literal
  60 [0x00000000 - 0x0000007f] [00000000.0bbbbbbb] -> 0bbbbbbb
  61 [0x00000080 - 0x000007ff] [00000bbb.bbbbbbbb] -> 110bbbbb, 10bbbbbb
  62 [0x00000800 - 0x0000ffff] [bbbbbbbb.bbbbbbbb] ->
  63         1110bbbb, 10bbbbbb, 10bbbbbb
  64 [0x00010000 - 0x001fffff] [00000000.000bbbbb.bbbbbbbb.bbbbbbbb] ->
  65         11110bbb, 10bbbbbb, 10bbbbbb, 10bbbbbb
  66 [0x00200000 - 0x03ffffff] [000000bb.bbbbbbbb.bbbbbbbb.bbbbbbbb] ->
  67         111110bb, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb
  68 [0x04000000 - 0x7fffffff] [0bbbbbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb] ->
  69         1111110b, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb
  70 .Ed
  71 .Pp
  72 If more than a single representation of a value exists (for example,
  73 0x00; 0xC0 0x80; 0xE0 0x80 0x80) the shortest representation is always
  74 used.
  75 Longer ones are detected as an error as they pose a potential
  76 security risk, and destroy the 1:1 character:octet sequence mapping.
  77 .Sh SEE ALSO
  78 .Xr euc 5
  79 .Rs
  80 .%A "Rob Pike"
  81 .%A "Ken Thompson"
  82 .%T "Hello World"
  83 .%J "Proceedings of the Winter 1993 USENIX Technical Conference"
  84 .%Q "USENIX Association"
  85 .%D "January 1993"
  86 .Re
  87 .Rs
  88 .%A "F. Yergeau"
  89 .%T "UTF-8, a transformation format of ISO 10646"
  90 .%O "RFC 2279"
  91 .%D "January 1998"
  92 .Re
  93 .Rs
  94 .%Q "The Unicode Consortium"
  95 .%T "The Unicode Standard, Version 3.0"
  96 .%D "2000"
  97 .%O "as amended by the Unicode Standard Annex #27: Unicode 3.1 and by the Unicode Standard Annex #28: Unicode 3.2"
  98 .Re
  99 .Sh STANDARDS
 100 The
 101 .Nm
 102 encoding is compatible with RFC 2279 and Unicode 3.2.