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.\" $DragonFly: src/lib/libc/locale/Attic/utf8.5,v 1.2 2003/06/17 04:26:44 dillon Exp $ 38.\" 39.Dd October 10, 2002 40.Dt UTF8 5 41.Os 42.Sh NAME 43.Nm utf8 44.Nd "UTF-8, a transformation format of ISO 10646" 45.Sh SYNOPSIS 46.Nm ENCODING 47.Qq UTF-8 48.Sh DESCRIPTION 49The 50.Nm UTF-8 51encoding represents UCS-4 characters as a sequence of octets, using 52between 1 and 6 for each character. 53It is backwards compatible with 54.Tn ASCII , 55so 0x00-0x7f refer to the 56.Tn ASCII 57character set. 58The multibyte encoding of non- 59.Tn ASCII 60characters 61consist entirely of bytes whose high order bit is set. 62The actual 63encoding is represented by the following table: 64.Bd -literal 65[0x00000000 - 0x0000007f] [00000000.0bbbbbbb] -> 0bbbbbbb 66[0x00000080 - 0x000007ff] [00000bbb.bbbbbbbb] -> 110bbbbb, 10bbbbbb 67[0x00000800 - 0x0000ffff] [bbbbbbbb.bbbbbbbb] -> 68 1110bbbb, 10bbbbbb, 10bbbbbb 69[0x00010000 - 0x001fffff] [00000000.000bbbbb.bbbbbbbb.bbbbbbbb] -> 70 11110bbb, 10bbbbbb, 10bbbbbb, 10bbbbbb 71[0x00200000 - 0x03ffffff] [000000bb.bbbbbbbb.bbbbbbbb.bbbbbbbb] -> 72 111110bb, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb 73[0x04000000 - 0x7fffffff] [0bbbbbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb] -> 74 1111110b, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb 75.Ed 76.Pp 77If more than a single representation of a value exists (for example, 780x00; 0xC0 0x80; 0xE0 0x80 0x80) the shortest representation is always 79used. 80Longer ones are detected as an error as they pose a potential 81security risk, and destroy the 1:1 character:octet sequence mapping. 82.Sh COMPATIBILITY 83The 84.Nm 85encoding supersedes the 86.Xr utf2 4 87encoding. 88The only differences between the two are that 89.Nm 90handles the full 31-bit character set of 91.Tn ISO 9210646 93whereas 94.Xr utf2 4 95is limited to a 16-bit character set, 96and that 97.Xr utf2 4 98accepts redundant, non-"shortest form" representations of characters. 99.Sh SEE ALSO 100.Xr euc 4 , 101.Xr utf2 4 102.Rs 103.%A "F. Yergeau" 104.%T "UTF-8, a transformation format of ISO 10646" 105.%O "RFC 2279" 106.%D "January 1998" 107.Re 108.Sh STANDARDS 109The 110.Nm 111encoding is compatible with RFC 2279. 112