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.\" $OpenBSD: utf8.7,v 1.7 2018/05/17 16:44:23 schwarze Exp $
.\"
.\" Copyright (c) 2017 Ted Unangst <tedu@openbsd.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate: May 17 2018 $
.Dt UTF8 7
.Os
.Sh NAME
.Nm utf8
.Nd UTF-8 text encoding
.Sh DESCRIPTION
UTF-8 is a multibyte character encoding for Unicode text.
It is the preferred format for non ASCII text.
.Pp
Unicode codepoints are encoded as follows:
.Bl -tag -width Ds
.It U+0000 \(en U+007F:
One byte: 0....... (compatible with ASCII)
.It U+0080 \(en U+07FF:
Two bytes: 110..... 10......
.It U+0800 \(en U+D7FF and U+E000 \(en U+FFFF:
Three bytes: 1110.... 10...... 10......
.It U+10000 \(en U+10FFFF:
Four bytes: 11110... 10...... 10...... 10......
.El
.Pp
The bits shown as dots contain the codepoint represented as a binary
integer.
.Pp
Bytes starting with the bit pattern 11...... are called UTF-8 start
bytes, and those starting with 10...... UTF-8 continuation bytes.
The number of leading 1 bits in a start byte indicates the total
number of bytes used to encode the codepoint, including the start
byte.
.Pp
Encodings using more bytes than required are invalid.
In particular, 11000000 and 11000001 are not valid start bytes,
the byte after 11100000 must be at least 10100000,
and the byte after 11110000 must be at least 10010000.
.Sh SEE ALSO
.Xr locale 1 ,
.Xr ascii 7
.Sh STANDARDS
.Rs
.%A F. Yergeau
.%D November 2003
.%R RFC 3629
.%T UTF-8, a transformation format of ISO 10646
.Re
.Pp
.Lk http://www.unicode.org/versions/latest/ "The Unicode Standard"
.Pp
.Lk http://www.unicode.org/reports/tr44/ "The Unicode Character Database"
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