1.\" Copyright (c) 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" This code is derived from software contributed to Berkeley by 5.\" Paul Borman at Krystal Technologies. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions 9.\" are met: 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in the 14.\" documentation and/or other materials provided with the distribution. 15.\" 3. All advertising materials mentioning features or use of this software 16.\" must display the following acknowledgement: 17.\" This product includes software developed by the University of 18.\" California, Berkeley and its contributors. 19.\" 4. Neither the name of the University nor the names of its contributors 20.\" may be used to endorse or promote products derived from this software 21.\" without specific prior written permission. 22.\" 23.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 24.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 25.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 26.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 27.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 28.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 29.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 30.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 32.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 33.\" SUCH DAMAGE. 34.\" 35.\" @(#)utf2.4 8.1 (Berkeley) 6/4/93 36.\" $FreeBSD: src/lib/libc/locale/utf8.5,v 1.1.2.1 2002/10/24 11:00:52 tjr Exp $ 37.\" 38.Dd October 10, 2002 39.Dt UTF8 5 40.Os 41.Sh NAME 42.Nm utf8 43.Nd "UTF-8, a transformation format of ISO 10646" 44.Sh SYNOPSIS 45.Nm ENCODING 46.Qq UTF-8 47.Sh DESCRIPTION 48The 49.Nm UTF-8 50encoding represents UCS-4 characters as a sequence of octets, using 51between 1 and 6 for each character. 52It is backwards compatible with 53.Tn ASCII , 54so 0x00-0x7f refer to the 55.Tn ASCII 56character set. 57The multibyte encoding of non- 58.Tn ASCII 59characters 60consist entirely of bytes whose high order bit is set. 61The actual 62encoding is represented by the following table: 63.Bd -literal 64[0x00000000 - 0x0000007f] [00000000.0bbbbbbb] -> 0bbbbbbb 65[0x00000080 - 0x000007ff] [00000bbb.bbbbbbbb] -> 110bbbbb, 10bbbbbb 66[0x00000800 - 0x0000ffff] [bbbbbbbb.bbbbbbbb] -> 67 1110bbbb, 10bbbbbb, 10bbbbbb 68[0x00010000 - 0x001fffff] [00000000.000bbbbb.bbbbbbbb.bbbbbbbb] -> 69 11110bbb, 10bbbbbb, 10bbbbbb, 10bbbbbb 70[0x00200000 - 0x03ffffff] [000000bb.bbbbbbbb.bbbbbbbb.bbbbbbbb] -> 71 111110bb, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb 72[0x04000000 - 0x7fffffff] [0bbbbbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb] -> 73 1111110b, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb 74.Ed 75.Pp 76If more than a single representation of a value exists (for example, 770x00; 0xC0 0x80; 0xE0 0x80 0x80) the shortest representation is always 78used. 79Longer ones are detected as an error as they pose a potential 80security risk, and destroy the 1:1 character:octet sequence mapping. 81.Sh COMPATIBILITY 82The 83.Nm 84encoding supersedes the 85.Xr utf2 4 86encoding. 87The only differences between the two are that 88.Nm 89handles the full 31-bit character set of 90.Tn ISO 9110646 92whereas 93.Xr utf2 4 94is limited to a 16-bit character set, 95and that 96.Xr utf2 4 97accepts redundant, non-"shortest form" representations of characters. 98.Sh SEE ALSO 99.Xr euc 4 , 100.Xr utf2 4 101.Rs 102.%A "F. Yergeau" 103.%T "UTF-8, a transformation format of ISO 10646" 104.%O "RFC 2279" 105.%D "January 1998" 106.Re 107.Sh STANDARDS 108The 109.Nm 110encoding is compatible with RFC 2279. 111