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utf8(5)

NAME

     utf8 -- UTF-8, a transformation format of ISO 10646

SYNOPSIS

     ENCODING "UTF-8"

DESCRIPTION

     The UTF-8 encoding represents UCS-4 characters as a sequence of octets,
     using between 1 and 6 for each character.	It is backwards compatible
     with ASCII, so 0x00-0x7f refer to the ASCII character set.  The multibyte
     encoding of non-ASCII characters consist entirely of bytes whose high
     order bit is set.	The actual encoding is represented by the following
     table:

     [0x00000000 - 0x0000007f] [00000000.0bbbbbbb] -> 0bbbbbbb
     [0x00000080 - 0x000007ff] [00000bbb.bbbbbbbb] -> 110bbbbb, 10bbbbbb
     [0x00000800 - 0x0000ffff] [bbbbbbbb.bbbbbbbb] ->
	     1110bbbb, 10bbbbbb, 10bbbbbb
     [0x00010000 - 0x001fffff] [00000000.000bbbbb.bbbbbbbb.bbbbbbbb] ->
	     11110bbb, 10bbbbbb, 10bbbbbb, 10bbbbbb
     [0x00200000 - 0x03ffffff] [000000bb.bbbbbbbb.bbbbbbbb.bbbbbbbb] ->
	     111110bb, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb
     [0x04000000 - 0x7fffffff] [0bbbbbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb] ->
	     1111110b, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb

     If more than a single representation of a value exists (for example,
     0x00; 0xC0 0x80; 0xE0 0x80 0x80) the shortest representation is always
     used.  Longer ones are detected as an error as they pose a potential
     security risk, and destroy the 1:1 character:octet sequence mapping.

COMPATIBILITY

     The utf8 encoding supersedes the utf2(5) encoding.  The only differences
     between the two are that utf8 handles the full 31-bit character set of
     ISO 10646 whereas utf2(5) is limited to a 16-bit character set, and that
     utf2(5) accepts redundant, non-``shortest form'' representations of char-
     acters.

SEE ALSO

     euc(5), utf2(5)

     Rob Pike and Ken Thompson, "Hello World", Proceedings of the Winter 1993
     USENIX Technical Conference, USENIX Association, January 1993.

     F. Yergeau, UTF-8, a transformation format of ISO 10646, January 1998,
     RFC 2279.

     The Unicode Standard, Version 3.0, The Unicode Consortium, 2000, as
     amended by the Unicode Standard Annex #27: Unicode 3.1 and by the Unicode
     Standard Annex #28: Unicode 3.2.

STANDARDS

     The utf8 encoding is compatible with RFC 2279 and Unicode 3.2.

FreeBSD 5.4			 April 7, 2004			   FreeBSD 5.4

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