Unicode - Wikipedia

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Character encoding standard
Unicode
Logo of the
Unicode Consortium
Alias(es)
Universal Coded Character Set
(UCS)
ISO/IEC 10646
Languages
168 scripts
list
Standard
Unicode Standard
Encoding formats
UTF-8
UTF-16
GB18030
UTF-32
BOCU
SCSU
UTF-EBCDIC
(uncommon)
UTF-7
UTF-1
(obsolete)
Preceded by
ISO/IEC 8859
, among others
Official website
Technical website
This article contains uncommon Unicode characters.
Without proper
rendering support
, you may see
question marks, boxes, or other symbols
Unicode
(also known as
The Unicode Standard
and
TUS
) is a
character encoding
standard maintained by the
Unicode Consortium
designed to support the use of text in all of the world's
writing systems
that can be digitized. Version 17.0
defines 159,801
characters
and 172
scripts
used in various ordinary, literary, academic and technical contexts.
Unicode has largely supplanted the previous environment of myriad incompatible
character sets
used within different locales and on different computer architectures. The entire repertoire of these sets, plus many additional characters, were merged into the single Unicode set. Unicode is used to encode the vast majority of text on the Internet, including most
web pages
, and relevant Unicode support has become a common consideration in contemporary software development. Unicode is ultimately capable of encoding more than 1.1 million characters.
The Unicode
character repertoire
is synchronized with
ISO/IEC 10646
, each being code-for-code identical with one another. However,
The Unicode Standard
is more than just a repertoire within which characters are assigned. To aid developers and designers, the standard also provides charts and reference data, as well as annexes explaining concepts germane to various scripts, providing guidance for their implementation. Topics covered by these annexes include
character normalization
character composition
and decomposition,
collation
, and
directionality
Unicode encodes 3,790
emoji
, with the continued development thereof conducted by the Consortium as a part of the standard.
The widespread adoption of Unicode was in large part responsible for the initial popularization of emoji outside of Japan.
citation needed
Unicode text is processed and stored as binary data
using one of several encodings
, which define how to translate the standard's abstracted codes for characters into sequences of bytes.
The Unicode Standard
itself defines three encodings:
UTF-8
UTF-16
and
UTF-32
, though several others exist. UTF-8 is the most widely used by a large margin, in part due to its backwards-compatibility with
ASCII
Origin and development
Unicode was originally designed with the intent of transcending limitations present in all text encodings designed up to that point: each encoding was relied upon for use in its own context, but with no particular expectation of compatibility with any other. Indeed, any two encodings chosen were often totally unworkable when used together, with text encoded in one
interpreted as garbage characters
by the other. Most encodings had only been designed to facilitate interoperation between a handful of scripts—often primarily between a given script and
Latin characters
—not between a large number of scripts, and not with all of the scripts supported being treated in a consistent manner.
The philosophy that underpins Unicode seeks to encode the underlying characters—
graphemes
and grapheme-like units—rather than graphical distinctions considered mere variant
glyphs
thereof, that are instead best handled by the
typeface
, through the use of
markup
, or by some other means. In particularly complex cases, such as
the treatment of orthographical variants in Han characters
, there is considerable disagreement regarding which differences justify their own encodings, and which are only graphical variants of other characters.
At the most abstract level, Unicode assigns a unique number called a
code point
to each character. Many issues of visual representation—including size, shape, and style—are intended to be up to the discretion of the software actually rendering the text, such as a
web browser
or
word processor
. However, partially with the intent of encouraging rapid adoption, the simplicity of this original model has become somewhat more elaborate over time, and various pragmatic concessions have been made over the course of the standard's development.
The first 256 code points mirror the
ISO/IEC 8859-1
standard, with the intent of trivializing the conversion of text already written in Western European scripts. To preserve the distinctions made by different legacy encodings, therefore allowing for conversion between them and Unicode without any loss of information, many
characters nearly identical to others
, in both appearance and intended function, were given distinct code points. For example, the
Halfwidth and Fullwidth Forms
block encompasses a full semantic duplicate of the Latin alphabet, because legacy
CJK encodings
contained both "fullwidth" (matching the width of CJK characters) and "halfwidth" (matching ordinary Latin script) characters.
History
The origins of Unicode can be traced back to the 1980s, to a group of individuals with connections to
Xerox
's
Character Code Standard
(XCCS).
In 1987, Xerox employee
Joe Becker
, along with
Apple
employees
Lee Collins
and
Mark Davis
, started investigating the practicalities of creating a universal character set.
With additional input from Peter Fenwick and
Dave Opstad
Becker published a draft proposal for an "international/multilingual text character encoding system in August 1988, tentatively called Unicode". He explained that "the name 'Unicode' is intended to suggest a unique, unified, universal encoding".
In this document, entitled
Unicode 88
, Becker outlined a scheme using
16-bit
characters:
Unicode is intended to address the need for a workable, reliable world text encoding. Unicode could be roughly described as "wide-body
ASCII
" that has been stretched to 16 bits to encompass the characters of all the world's living languages. In a properly engineered design, 16 bits per character are more than sufficient for this purpose.
This design decision was made based on the assumption that only scripts and characters in "modern" use would require encoding:
Unicode gives higher priority to ensuring utility for the future than to preserving past antiquities. Unicode aims in the first instance at the characters published in the modern text (e.g. in the union of all newspapers and magazines printed in the world in 1988), whose number is undoubtedly far below 2
14
= 16,384. Beyond those modern-use characters, all others may be defined to be obsolete or rare; these are better candidates for private use registration than for congesting the public list of generally useful Unicode.
In early 1989, the Unicode working group expanded to include Ken Whistler and Mike Kernaghan of Metaphor, Karen Smith-Yoshimura and Joan Aliprand of
Research Libraries Group
, and Glenn Wright of
Sun Microsystems
. The Research Libraries Group had an existing solution for East Asian character sets, which became one of the inputs to the Unicode character set.
In 1990, Michel Suignard and Asmus Freytag of
Microsoft
and
NeXT
's Rick McGowan had also joined the group. By the end of 1990, most of the work of remapping existing standards had been completed, and a final review draft of Unicode was ready.
The
Unicode Consortium
was incorporated in California on 3 January 1991,
and the first volume of
The Unicode Standard
was published that October. The second volume, now adding Han ideographs, was published in June 1992.
In 1996, a surrogate character mechanism was implemented in Unicode 2.0, so that Unicode was no longer restricted to 16 bits. This increased the Unicode codespace to over a million code points, which allowed for the encoding of many historic scripts, such as
Egyptian hieroglyphs
, and thousands of rarely used or obsolete characters that had not been anticipated for inclusion in the standard. Among these characters are various rarely used
CJK characters
—many mainly being used in proper names, making them far more necessary for a universal encoding than the original Unicode architecture envisioned.
Unicode Consortium
Main article:
Unicode Consortium
The Unicode Consortium is a non-profit organization that coordinates Unicode's development. Full members include most of the main computer software and hardware companies (and few others) with any interest in text-processing standards, including
Adobe
Apple
Google
IBM
Meta
(previously as Facebook),
Microsoft
Netflix
, and
SAP
10
Over the years several countries or government agencies have been members of the Unicode Consortium.
10
The Consortium has the ambitious goal of eventually replacing existing character encoding schemes with Unicode and its standard Unicode Transformation Format (UTF) schemes, as many of the existing schemes are limited in size and scope and are incompatible with
multilingual
environments.
The
Unicode Bulldog Award
is given to people deemed to be influential in Unicode's development, with recipients including
Tatsuo Kobayashi
, Thomas Milo, Roozbeh Pournader,
Ken Lunde
, and
Michael Everson
11
Scripts covered
Main article:
Script (Unicode)
Many modern applications can render a substantial subset of the many
scripts in Unicode
, as demonstrated by this screenshot from the
OpenOffice.org
application.
As of September 2025
[update]
, a total of 172
12
scripts
alphabets
abugidas
and
syllabaries
) are included in Unicode, covering most major
writing systems
in use today.
13
14
There are still scripts that are not yet encoded, particularly those mainly used in historical, liturgical, and academic contexts. Further additions of characters to the already encoded scripts, as well as
symbols
, in particular for mathematics and
music
also occur.
Proposals for adding scripts
The Unicode Roadmap Committee (
Michael Everson
, Rick McGowan, Ken Whistler, V.S. Umamaheswaran)
15
maintain the list of scripts that are candidates or potential candidates for encoding and their tentative code block assignments on the Unicode Roadmap
16
page of the
Unicode Consortium
website. For some scripts on the Roadmap, such as
Jurchen
and
Khitan large script
, encoding proposals have been made and they are working their way through the approval process. For other scripts, such as
Numidian
and
Rongorongo
, no proposal has yet been made, and they await agreement on character repertoire and other details from the user communities involved.
Some modern invented scripts which have not yet been included in Unicode (e.g.,
Tengwar
) or which do not qualify for inclusion in Unicode due to lack of real-world use (e.g.,
Klingon
) are listed in the
ConScript Unicode Registry
, along with unofficial but widely used
private use area
code assignments.
There is also a
Medieval Unicode Font Initiative
focused on special Latin medieval characters. Part of these proposals has been already included in Unicode.
The Script Encoding Initiative (SEI),
17
a project created by Deborah Anderson at the
University of California, Berkeley
, was founded in 2002 with the goal of funding proposals for scripts not yet encoded in the standard. Now run by Anushah Hossain, SEI has become a major source of proposed additions to the standard in recent years.
18
Although SEI collaborates with the Unicode Consortium and the ISO/IEC 10646 standards process, it operates independently, supporting the technical, linguistic, and historical research needed to prepare formal proposals. SEI maintains a database of scripts that have yet to be encoded in the Unicode Standard on the project's website.
19
Versions
The Unicode Consortium together with the ISO have developed a shared
repertoire
following the initial publication of
The Unicode Standard
: Unicode and the ISO's
Universal Coded Character Set
(UCS) use identical character names and code points. However, the Unicode versions do differ from their ISO equivalents in two significant ways.
While the UCS is a simple character map, Unicode specifies the rules, algorithms, and properties necessary to achieve interoperability between different platforms and languages. Thus,
The Unicode Standard
includes more information, covering in-depth topics such as bitwise encoding,
collation
, and rendering. It also provides a comprehensive catalog of character properties, including those needed for supporting
bidirectional text
, as well as visual charts and reference data sets to aid implementers. Previously,
The Unicode Standard
was sold as a print volume containing the complete core specification, standard annexes,
note 1
and code charts. However, version 5.0, published in 2006, was the last version printed this way. Starting with version 5.2, only the core specification, published as a print-on-demand paperback, may be purchased.
20
The full text, on the other hand, is published as a free PDF on the Unicode website.
A practical reason for this publication method highlights the second significant difference between the UCS and Unicode—the frequency with which updated versions are released and new characters added.
The Unicode Standard
has regularly released annual expanded versions, occasionally with more than one version released in a calendar year and with rare cases where the scheduled release had to be postponed. For instance, in April 2020, a month after version 13.0 was published, the Unicode Consortium announced they had changed the intended release date for version 14.0, pushing it back six months to September 2021 due to the
COVID-19 pandemic
Thus far, the following versions of
The Unicode Standard
have been published. Update versions, which do not include any changes to character repertoire, are signified by the third number (e.g., "version 4.0.1") and are omitted in the table below.
21
Unicode version history and notable changes to characters and scripts
Ver­sion
Date
Publication
(book, text)
UCS
edition
Total
Details
Scripts
Characters
1.0.0
22
October 1991
ISBN
0-201-56788-1
(vol. 1)
N/a
24
7129
Initial scripts covered:
Arabic
Armenian
Bengali
Bopomofo
Cyrillic
Devanagari
Georgian
Greek and Coptic
Gujarati
Gurmukhi
Hangul
Hebrew
Hiragana
Kannada
Katakana
Lao
Latin
Malayalam
Odia
Tamil
Telugu
Thai
, and
Tibetan
1.0.1
23
June 1992
ISBN
0-201-60845-6
(vol. 2)
25
28
327
+21
204
−6
The initial 20,902
CJK Unified Ideographs
1.1
24
June 1993
N/a
ISO/IEC 10646
-1:1993
24
34
168
+5963
−9
33 reclassified as control characters. 4,306
Hangul
syllables,
Tibetan
removed
2.0
25
July 1996
ISBN
0-201-48345-9
25
38
885
+11
373
−6656
Original set of Hangul syllables removed, new set of 11,172 Hangul syllables added at new location, Tibetan added back in a new location and with a different character repertoire, Surrogate character mechanism defined, Plane 15 and Plane 16
private use area
allocated
2.1
26
May 1998
N/a
38
887
+2
U+20AC
EURO SIGN
U+FFFC
OBJECT REPLACEMENT CHARACTER
26
3.0
27
September 1999
ISBN
0-201-61633-5
ISO/IEC 10646-1:2000
38
49
194
+10
307
Cherokee
Geʽez
Khmer
Mongolian
Burmese
Ogham
runes
Sinhala
Syriac
Thaana
Canadian Aboriginal syllabics
, and
Yi Syllables
Braille
patterns
3.1
28
March 2001
N/a
ISO/IEC 10646-1:2000
ISO/IEC 10646-2:2001
41
94
140
+44
946
Deseret
Gothic
and
Old Italic
, sets of symbols for Western and
Byzantine music
, 42,711 additional CJK Unified Ideographs
3.2
29
March 2002
45
95
156
+1016
Philippine
scripts (
Buhid
Hanunoo
Tagalog
, and
Tagbanwa
), mathematical symbols
4.0
30
April 2003
ISBN
0-321-18578-1
ISO/IEC 10646:2003
52
96
382
+1226
Cypriot syllabary
Limbu
Linear B
Osmanya
Shavian
Tai Le
, and
Ugaritic
Hexagram symbols
4.1
31
March 2005
N/a
59
97
655
+1273
Buginese
Glagolitic
Kharosthi
New Tai Lue
Old Persian
Sylheti Nagri
, and
Tifinagh
Coptic
disunified from Greek, ancient
Greek numbers
and
musical symbols
, first named character sequences were introduced.
32
5.0
33
July 2006
ISBN
0-321-48091-0
64
99
024
+1369
Balinese
cuneiform
N'Ko
ʼPhags-pa
Phoenician
34
5.1
35
April 2008
N/a
75
100
648
+1624
Carian
Cham
Kayah Li
Lepcha
Lycian
Lydian
Ol Chiki
Rejang
Saurashtra
Sundanese
, and
Vai
, sets of symbols for the
Phaistos Disc
Mahjong
tiles,
Domino tiles
, additions to Burmese,
Scribal abbreviations
U+1E9E
LATIN CAPITAL LETTER SHARP S
5.2
36
October 2009
ISBN
978-1-936213-00-9
90
107
296
+6648
Avestan
Bamum
Gardiner's sign list
of
Egyptian hieroglyphs
Imperial Aramaic
Inscriptional Pahlavi
Inscriptional Parthian
Javanese
Kaithi
Lisu
Meetei Mayek
Old South Arabian
Old Turkic
Samaritan
Tai Tham
and
Tai Viet
, additional CJK Unified Ideographs, Jamo for Old Hangul,
Vedic Sanskrit
6.0
37
October 2010
ISBN
978-1-936213-01-6
ISO/IEC 10646:2010
93
109
384
+2088
Batak
Brahmi
Mandaic
playing card
symbols, transport and map symbols,
alchemical symbols
emoticons
and emoji,
38
additional CJK Unified Ideographs
6.1
39
January 2012
ISBN
978-1-936213-02-3
ISO/IEC 10646:2012
100
110
116
+732
Chakma
Meroitic cursive
Meroitic hieroglyphs
Miao
Sharada
Sora Sompeng
, and
Takri
6.2
40
September 2012
ISBN
978-1-936213-07-8
110
117
+1
U+20BA
TURKISH LIRA SIGN
6.3
41
September 2013
ISBN
978-1-936213-08-5
110
122
+5
5 bidirectional formatting characters
7.0
42
June 2014
ISBN
978-1-936213-09-2
123
112
956
+2834
Bassa Vah
Caucasian Albanian
Duployan
Elbasan
Grantha
Khojki
Khudawadi
Linear A
Mahajani
Manichaean
Mende Kikakui
Modi
Mro
Nabataean
Old North Arabian
Old Permic
Pahawh Hmong
Palmyrene
Pau Cin Hau
Psalter Pahlavi
Siddham
Tirhuta
Warang Citi
, and
dingbats
8.0
43
June 2015
ISBN
978-1-936213-10-8
ISO/IEC 10646:2014
129
120
672
+7716
Ahom
Anatolian hieroglyphs
Hatran
Multani
Old Hungarian
SignWriting
, additional CJK Unified Ideographs, lowercase letters for Cherokee, 5 emoji
skin tone modifiers
9.0
46
June 2016
ISBN
978-1-936213-13-9
135
128
172
+7500
Adlam
Bhaiksuki
Marchen
Newa
Osage
Tangut
, 72 emoji
47
10.0
48
June 2017
ISBN
978-1-936213-16-0
ISO/IEC 10646:2017
139
136
690
+8518
Zanabazar Square
Soyombo
Masaram Gondi
Nüshu
hentaigana
, 7,494 CJK Unified Ideographs, 56 emoji,
U+20BF
BITCOIN SIGN
11.0
49
June 2018
ISBN
978-1-936213-19-1
146
137
374
+684
Dogra
Georgian Mtavruli
capital letters,
Gunjala Gondi
Hanifi Rohingya
Indic Siyaq Numbers
Makasar
Medefaidrin
Old Sogdian and Sogdian
Maya numerals
, 5 CJK Unified Ideographs, symbols for
xiangqi
and
star ratings
, 145 emoji
12.0
50
March 2019
ISBN
978-1-936213-22-1
150
137
928
+554
Elymaic
Nandinagari
Nyiakeng Puachue Hmong
Wancho
Miao script
, hiragana and katakana small letters, Tamil historic fractions and symbols, Lao letters for
Pali
, Latin letters for Egyptological and Ugaritic transliteration, hieroglyph format controls, 61 emoji
12.1
51
May 2019
ISBN
978-1-936213-25-2
137
929
+1
U+32FF
SQUARE ERA NAME REIWA
13.0
52
March 2020
ISBN
978-1-936213-26-9
ISO/IEC 10646:2020
53
154
143
859
+5930
Chorasmian
Dhives Akuru
Khitan small script
Yezidi
, 4,969 CJK ideographs, Arabic script additions used to write
Hausa
Wolof
, and other African languages, additions used to write
Hindko
and
Punjabi
in Pakistan, Bopomofo additions used for Cantonese, Creative Commons license symbols, graphic characters for compatibility with teletext and home computer systems, 55 emoji
14.0
54
September 2021
ISBN
978-1-936213-29-0
159
144
697
+838
Toto
Cypro-Minoan
Vithkuqi
Old Uyghur
Tangsa
, extended IPA, Arabic script additions for use in languages across Africa and in Iran, Pakistan, Malaysia, Indonesia, Java, and Bosnia, additions for honorifics and Quranic use, additions to support languages in North America, the Philippines, India, and Mongolia,
U+20C0
SOM SIGN
Znamenny
musical notation, 37 emoji
15.0
55
September 2022
ISBN
978-1-936213-32-0
161
149
186
+4489
Kawi
and
Mundari
, 20 emoji, 4,192 CJK ideographs, control characters for Egyptian hieroglyphs
15.1
56
September 2023
ISBN
978-1-936213-33-7
149
813
+627
Additional CJK ideographs
16.0
57
September 2024
ISBN
978-1-936213-34-4
168
154
998
+5185
Garay
Gurung Khema
Kirat Rai
Ol Onal
Sunuwar
Todhri
Tulu-Tigalari
, 7 emoji, 3,995 Egyptian Hieroglyphs
17.0
58
September 2025
ISBN
978-1-936213-35-1
172
159
801
+4803
Beria Erfe
Tai Yo
Sidetic
Tolong Siki
U+20C1
SAUDI RIYAL SIGN
, 7 emoji, 4,316 CJK unified ideographs
A large amount of documentation for Windows incorrectly uses the term "Unicode" to mean
only
the UTF-16 encoding.
The total number of graphic and format characters, excluding
private use characters
control characters
noncharacters
, and
surrogate code points
).
2.0 added Amendments 5, 6, and 7
2.1 added two characters from Amendment 18.
3.2 added Amendment 1.
4.1 added Amendment 1
5.0 added Amendment 2 as well as four characters from Amendment 3
5.1 added Amendment 4
5.2 added Amendments 5 and 6
Plus the
Indian rupee sign
6.2 added the
Turkish lira sign
6.3 added five additional characters
7.0 added Amendments 1 and 2 as well as the
ruble sign
Plus Amendment 1, as well as the
Lari sign
, nine CJK unified ideographs, and 41 emoji;
44
9.0 added Amendment 2, as well as Adlam, Newa, Japanese TV symbols, and 74 emoji and symbols.
45
Plus 56 emoji, 285
hentaigana
characters, and 3 Zanabazar Square characters
11.0 added 46 Mtavruli Georgian capital letters, 5 CJK unified ideographs, and 66 emoji
12.0 added 62 additional characters.
Architecture and terminology
See also:
Universal Character Set characters
Codespace and code points
The Unicode Standard
defines a
codespace
59
a sequence of integers called
code points
60
in the range from 0 to
114
111
, notated according to the standard as
U+0000
U+10FFFF
61
The codespace is a systematic, architecture-independent representation of
The Unicode Standard
; actual text is processed as binary data via one of several Unicode encodings, such as
UTF-8
In this normative notation, the two-character prefix
U+
always precedes a written code point, and the code points themselves are written as
hexadecimal
numbers.
note 2
At least four hexadecimal digits are always written, with
leading zeros
prepended as needed. For example, the code point
U+00F7
DIVISION SIGN
is padded with two leading zeros, but
U+13254
EGYPTIAN HIEROGLYPH O004
) is not padded.
63
There are a total of
112
064
valid code points within the codespace.
64
This number arises from the limitations of the
UTF-16
character encoding, which can encode the 2
16
code points in the range
U+0000
through
U+FFFF
except for the 2
11
code points in the range
U+D800
through
U+DFFF
, which are used as surrogate pairs to encode the 2
20
code points in the range
U+10000
through
U+10FFFF
Code planes and blocks
Main article:
Plane (Unicode)
The Unicode codespace is divided into 17
planes
, numbered 0 to 16. Plane 0 is the
Basic Multilingual Plane
(BMP), and contains the most commonly used characters. All code points in the BMP are accessed as a single code unit in UTF-16 encoding and can be encoded in one, two or three bytes in UTF-8. Code points in planes 1 through 16 (the
supplementary planes
) are accessed as surrogate pairs in
UTF-16
and encoded in four bytes in
UTF-8
Within each plane, characters are allocated within named
blocks
of related characters. The size of a block is always a multiple of 16, and is often a multiple of 128, but is otherwise arbitrary. Characters required for a given script may be spread out over several different, potentially disjunct blocks within the codespace.
General Category property
Each code point is assigned a classification, listed as the code point's
General Category
property. Here, at the uppermost level code points are categorized as one of Letter, Mark, Number, Punctuation, Symbol, Separator, or Other. Under each category, each code point is then further subcategorized. In most cases, other properties must be used to adequately describe all the characteristics of any given code point.
General Category
(Unicode
Character Property
Value
Category Major, minor
Basic type
Character assigned
Count
(as of 17.0)
Remarks
, Letter;
LC
, Cased Letter
(Lu, Ll, and Lt only)
Lu
Letter, uppercase
Graphic
Character
1,886
Ll
Letter, lowercase
Graphic
Character
2,283
Lt
Letter, titlecase
Graphic
Character
31
Digraphs
consisting of an uppercase letter followed by a lowercase letter (e.g.,
, and
Lm
Letter, modifier
Graphic
Character
410
modifier letter
Lo
Letter, other
Graphic
Character
141,062
An
ideograph
or a letter in a
unicase alphabet
, Mark
Mn
Mark, nonspacing
Graphic
Character
2,059
Mc
Mark, spacing combining
Graphic
Character
471
Me
Mark, enclosing
Graphic
Character
13
, Number
Nd
Number, decimal digit
Graphic
Character
770
All these, and only these, have
Numeric Type
= De
Nl
Number, letter
Graphic
Character
239
Numerals composed of letters or letterlike symbols (e.g.,
Roman numerals
No
Number, other
Graphic
Character
915
E.g.,
vulgar fractions
superscript
and
subscript
digits, vigesimal digits
, Punctuation
Pc
Punctuation, connector
Graphic
Character
10
Includes spacing
underscore
characters such as "_", and other spacing
tie characters
. Unlike other punctuation characters, these may be classified as "word" characters by
regular expression
libraries.
Pd
Punctuation, dash
Graphic
Character
27
Includes several
hyphen
characters
Ps
Punctuation, open
Graphic
Character
79
Opening
bracket
characters
Pe
Punctuation, close
Graphic
Character
77
Closing bracket characters
Pi
Punctuation, initial quote
Graphic
Character
12
Opening
quotation mark
. Does not include the ASCII "neutral" quotation mark. May behave like Ps or Pe depending on usage
Pf
Punctuation, final quote
Graphic
Character
10
Closing quotation mark. May behave like Ps or Pe depending on usage
Po
Punctuation, other
Graphic
Character
641
, Symbol
Sm
Symbol, math
Graphic
Character
960
Mathematical symbols
(e.g.,
). Does not include parentheses and brackets, which are in categories Ps and Pe. Also does not include
, or
, which despite frequent use as mathematical operators, are primarily considered to be "punctuation".
Sc
Symbol, currency
Graphic
Character
64
Currency symbols
Sk
Symbol, modifier
Graphic
Character
125
So
Symbol, other
Graphic
Character
7,468
, Separator
Zs
Separator, space
Graphic
Character
17
Includes the space, but not
TAB
CR
, or
LF
, which are Cc
Zl
Separator, line
Format
Character
Only
U+2028
LINE SEPARATOR
(LSEP)
Zp
Separator, paragraph
Format
Character
Only
U+2029
PARAGRAPH SEPARATOR
(PSEP)
, Other
Cc
Other, control
Control
Character
65 (will never change)
No name,

Cf
Other, format
Format
Character
170
Includes the
soft hyphen
, joining control characters (
ZWNJ
and
ZWJ
), control characters to support
bidirectional text
, and
language tag
characters
Cs
Other, surrogate
Surrogate
Not (only used in
UTF-16
2,048 (will never change)
No name,

Co
Other, private use
Private-use
Character (but no interpretation specified)
137,468 total (will never change)
6,400 in
BMP
, 131,068
in
Planes 15–16
No name,

Cn
Other, not assigned
Noncharacter
Not
66 (will not change unless the range of Unicode code points is expanded)
No name,

Reserved
Not
814,664
No name,

"Table 4-4: General Category"
The Unicode Standard
. Unicode Consortium. September 2025.
"Table 2-3: Types of code points"
The Unicode Standard
. Unicode Consortium. September 2025.
"DerivedGeneralCategory.txt"
. The Unicode Consortium. 2025-07-24.
"5.7.1 General Category Values"
UTR #44: Unicode Character Database
. Unicode Consortium. 2024-08-27.
Unicode Character Encoding Stability Policies: Property Value Stability
Stability policy: Some gc groups will never change. gc=Nd corresponds with Numeric Type=De (decimal).
"Annex C: Compatibility Properties (§ word)"
Unicode Regular Expressions
. Version 23.
Unicode Consortium
. 2022-02-08. Unicode Technical Standard #18.
"Table 4-9: Construction of Code Point Labels"
The Unicode Standard
. Unicode Consortium. September 2025.
Code Point Label
may be used to identify a nameless code point. E.g. hhhh
>, . The Name remains blank, which can prevent inadvertently replacing, in documentation, a Control Name with a true Control code. Unicode also uses for .
The
1024
points in the range
U+D800
U+DBFF
are known as
high-surrogate
code points, and code points in the range
U+DC00
U+DFFF
1024
code points) are known as
low-surrogate
code points. A high-surrogate code point followed by a low-surrogate code point forms a
surrogate pair
in UTF-16 in order to represent code points greater than
U+FFFF
. In principle, these code points cannot otherwise be used, though in practice this rule is often ignored, especially when not using UTF-16.
A small set of code points are guaranteed never to be assigned to characters, although third-parties may make independent use of them at their discretion. There are 66 of these
noncharacters
U+FDD0
U+FDEF
and the last two code points in each of the 17 planes (e.g.
U+FFFE
U+FFFF
U+1FFFE
U+1FFFF
, ...,
U+10FFFE
U+10FFFF
). The set of noncharacters is stable, and no new noncharacters will ever be defined.
65
Like surrogates, the rule that these cannot be used is often ignored, although the operation of the
byte order mark
assumes that
U+FFFE
will never be the first code point in a text. The exclusion of surrogates and noncharacters leaves
111
998
code points available for use.
Private use
code points are considered to be assigned, but they intentionally have no interpretation specified by
The Unicode Standard
66
such that any interchange of such code points requires an independent agreement between the sender and receiver as to their interpretation. There are three private use areas in the Unicode codespace:
Private Use Area:
U+E000
U+F8FF
6400
characters),
Supplementary Private Use Area-A:
U+F0000
U+FFFFD
65
534
characters),
Supplementary Private Use Area-B:
U+100000
U+10FFFD
65
534
characters).
Graphic
characters are those defined by
The Unicode Standard
to have particular semantics, either having a visible
glyph
shape or representing a visible space. As of Unicode 17.0, there are
159
629
graphic characters.
Format
characters are characters that do not have a visible appearance but may have an effect on the appearance or behavior of neighboring characters. For example,
U+200C
ZERO WIDTH NON-JOINER
and
U+200D
ZERO WIDTH JOINER
may be used to change the default shaping behavior of adjacent characters (e.g. to inhibit ligatures or request ligature formation). There are 172 format characters in Unicode 17.0.
65 code points, the ranges
U+0000
U+001F
and
U+007F
U+009F
, are reserved as
control codes
, corresponding to the
C0 and C1 control codes
as defined in
ISO/IEC 6429
U+0009
TAB
U+000A
LINE FEED
, and
U+000D
CARRIAGE RETURN
are widely used in texts using Unicode. In a phenomenon known as
mojibake
, the C1 code points are improperly decoded according to the
Windows-1252
codepage, previously widely used in Western European contexts.
Together, graphic, format, control code, and private use characters are collectively referred to as
assigned characters
Reserved
code points are those code points that are valid and available for use, but have not yet been assigned. As of Unicode 17.0, there are
814
664
reserved code points.
Abstract characters
Further information:
Universal Character Set characters § Characters, grapheme clusters and glyphs
The set of graphic and format characters defined by Unicode does not correspond directly to the repertoire of
abstract characters
representable under Unicode. Unicode encodes characters by associating an abstract character with a particular code point.
67
However, not all abstract characters are encoded as a single Unicode character, and some abstract characters may be represented in Unicode by a sequence of two or more characters. For example, a Latin small letter "i" with an
ogonek
, a
dot above
, and an
acute accent
, which is required in
Lithuanian
, is represented by the character sequence
U+012F
U+0307
U+0301
. Unicode maintains a list of uniquely named character sequences for abstract characters that are not directly encoded in Unicode.
68
All assigned characters have a unique and immutable name by which they are identified. This immutability has been guaranteed since version 2.0 of
The Unicode Standard
by its Name Stability policy.
65
In cases where a name is seriously defective and misleading, or has a serious typographical error, a formal
alias
may be defined that applications are encouraged to use in place of the official character name. For example,
U+A015
YI SYLLABLE WU
has the formal alias
YI SYLLABLE ITERATION MARK
, and
U+FE18
PRESENTATION FORM FOR VERTICAL RIGHT WHITE LENTICULAR BRAKCET
sic
) has the formal alias
PRESENTATION FORM FOR VERTICAL RIGHT WHITE LENTICULAR BRA
CK
ET
69
Precomposed vis-à-vis composite characters
Unicode includes a mechanism for modifying characters that greatly extends the supported repertoire of glyphs. This covers the use of
combining diacritical marks
that may be added after the base character by the user. Multiple combining diacritics may be simultaneously applied to the same character. Unicode also contains
precomposed
versions of most letter/diacritic combinations in normal use. These make the conversion to and from legacy encodings simpler, and allow applications to use Unicode as an internal text format without having to implement combining characters. For example,
can be represented in Unicode as
U+0065
LATIN SMALL LETTER E
followed by
U+0301
◌́
COMBINING ACUTE ACCENT
, and equivalently as the precomposed character
U+00E9
LATIN SMALL LETTER E WITH ACUTE
. Thus, users often have multiple equivalent ways of encoding the same character. The mechanism of
canonical equivalence
within
The Unicode Standard
ensures the practical interchangeability of these equivalent encodings.
An example of this arises with the Korean alphabet
Hangul
: Unicode provides a mechanism for composing Hangul syllables from their individual
Hangul Jamo
subcomponents. However, it also provides
11
172
combinations of precomposed syllables made from the most common jamo.
CJK characters
presently only have codes for uncomposable radicals and precomposed forms. Most Han characters have either been intentionally composed from, or reconstructed as compositions of, simpler orthographic elements called
radicals
, so in principle Unicode could have enabled their composition as it did with Hangul. While this could have greatly reduced the number of required code points, as well as allowing the algorithmic synthesis of many arbitrary new characters, the complexities of character etymologies and the post-hoc nature of radical systems add immense complexity to the proposal. Indeed, attempts to design CJK encodings on the basis of composing radicals have been met with difficulties resulting from the reality that Chinese characters do not decompose as simply or as regularly as Hangul does.
The
CJK Radicals Supplement
block is assigned to the range
U+2E80
U+2EFF
, and the
Kangxi radicals
are assigned to
U+2F00
U+2FDF
. The
Ideographic Description Sequences
block covers the range
U+2FF0
U+2FFB
, but
The Unicode Standard
warns against using its characters as an alternate representation for characters encoded elsewhere:
This process is different from a formal
encoding
of an ideograph. There is no canonical description of unencoded ideographs; there is no semantic assigned to described ideographs; there is no equivalence defined for described ideographs. Conceptually, ideographic descriptions are more akin to the English phrase "an 'e' with an acute accent on it" than to the character sequence .
Ligatures
The
Devanāgarī
ddhrya
-ligature (द् + ध् + र् + य = द्ध्र्य) of JanaSanskritSans
70
The
Arabic
lām
alif
ligature (
‎+‎
‎=‎
لا
Many scripts, including
Arabic
and
Devanāgarī
, have special orthographic rules that require certain combinations of letterforms to be combined into special
ligature forms
. The rules governing ligature formation can be quite complex, requiring special script-shaping technologies such as ACE (Arabic Calligraphic Engine by DecoType in the 1980s and used to generate all the Arabic examples in the printed editions of
The Unicode Standard
), which became the
proof of concept
for
OpenType
(by Adobe and Microsoft),
Graphite
(by
SIL International
), or
AAT
(by Apple).
Instructions are also embedded in fonts to tell the operating system how to properly output different character sequences. A simple solution to the placement of combining marks or diacritics is assigning the marks a width of zero and placing the glyph itself to the left or right of the left sidebearing (depending on the direction of the script they are intended to be used with). A mark handled this way will appear over whatever character precedes it, but will not adjust its position relative to the width or height of the base glyph; it may be visually awkward and it may overlap some glyphs. Real stacking is impossible but can be approximated in limited cases (for example, Thai top-combining vowels and tone marks can just be at different heights to start with). Generally, this approach is only effective in monospaced fonts but may be used as a fallback rendering method when more complex methods fail.
Standardized subsets
Several subsets of Unicode are standardized: Microsoft Windows since
Windows NT 4.0
supports
WGL-4
with 657 characters, which is considered to support all contemporary European languages using the Latin, Greek, or Cyrillic script. Other standardized subsets of Unicode include the Multilingual European Subsets:
71
MES-1 (Latin scripts only; 335 characters), MES-2 (Latin, Greek, and Cyrillic; 1062 characters)
72
and MES-3A & MES-3B (two larger subsets, not shown here). MES-2 includes every character in MES-1 and WGL-4.
The standard
DIN 91379
73
specifies a subset of Unicode letters, special characters, and sequences of letters and diacritic signs to allow the correct representation of names and to simplify data exchange in Europe. This standard supports all of the official languages of all European Union countries, as well as the German minority languages and the official languages of Iceland, Liechtenstein, Norway, and Switzerland. To allow the transliteration of names in other writing systems to the Latin script according to the relevant ISO standards, all necessary combinations of base letters and diacritic signs are provided.
WGL-4
MES-1
and MES-2
Row
Cells
Range(s)
00
20–7E
Basic Latin
(00–7F)
A0–FF
Latin-1 Supplement
(80–FF)
01
00–13,
14–15,
16–2B,
2C–2D,
2E–4D,
4E–4F,
50–7E,
7F
Latin Extended-A
(00–7F)
8F,
92,
B7, DE-EF,
FA–FF
Latin Extended-B
(80–FF
...
02
18–1B, 1E–1F
Latin Extended-B (
...
00–4F)
59, 7C, 92
IPA Extensions
(50–AF)
BB–BD,
C6,
C7,
C9,
D6,
D8–DB,
DC,
DD,
DF, EE
Spacing Modifier Letters
(B0–FF)
03
74–75, 7A, 7E,
84–8A, 8C, 8E–A1, A3–CE,
D7, DA–E1
Greek
(70–FF)
04
00–5F, 90–91,
92–C4, C7–C8, CB–CC, D0–EB, EE–F5, F8–F9
Cyrillic
(00–FF)
1E
02–03, 0A–0B, 1E–1F, 40–41, 56–57, 60–61, 6A–6B,
80–85,
9B,
F2–F3
Latin Extended Additional
(00–FF)
1F
00–15, 18–1D, 20–45, 48–4D, 50–57, 59, 5B, 5D, 5F–7D, 80–B4, B6–C4, C6–D3, D6–DB, DD–EF, F2–F4, F6–FE
Greek Extended
(00–FF)
20
13–14,
15,
17,
18–19,
1A–1B,
1C–1D,
1E, 20–22, 26, 30, 32–33, 39–3A, 3C, 3E, 44,
4A
General Punctuation
(00–6F)
7F
, 82
Superscripts and Subscripts
(70–9F)
A3–A4, A7,
AC,
AF
Currency Symbols
(A0–CF)
21
05, 13, 16,
22, 26,
2E
Letterlike Symbols
(00–4F)
5B–5E
Number Forms
(50–8F)
90–93,
94–95, A8
Arrows
(90–FF)
22
00,
02,
03,
06,
08–09,
0F, 11–12, 15, 19–1A, 1E–1F,
27–28,
29,
2A,
2B, 48,
59,
60–61, 64–65,
82–83, 95, 97
Mathematical Operators
(00–FF)
23
02, 0A, 20–21,
29–2A
Miscellaneous Technical
(00–FF)
25
00, 02, 0C, 10, 14, 18, 1C, 24, 2C, 34, 3C, 50–6C
Box Drawing
(00–7F)
80, 84, 88, 8C, 90–93
Block Elements
(80–9F)
A0–A1, AA–AC, B2, BA, BC, C4, CA–CB, CF, D8–D9, E6
Geometric Shapes
(A0–FF)
26
3A–3C, 40, 42, 60, 63, 65–66,
6A,
6B
Miscellaneous Symbols
(00–FF)
F0
(01–02)
Private Use Area
(00–FF ...)
FB
01–02
Alphabetic Presentation Forms
(00–4F)
FF
FD
Specials
Rendering software that cannot process a Unicode character appropriately often displays it as an open rectangle, or as
U+FFFD
to indicate the position of the unrecognized character. Some systems have made attempts to provide more information about such characters. Apple's
Last Resort font
will display a substitute glyph indicating the Unicode range of the character, and the
SIL International
's
Unicode fallback font
will display a box showing the hexadecimal scalar value of the character.
Mapping and encodings
Several mechanisms have been specified for storing a series of code points as a series of bytes.
Unicode defines two mapping methods: the
Unicode Transformation Format
(UTF) encodings, and the
Universal Coded Character Set
(UCS) encodings. An encoding maps (possibly a subset of) the range of Unicode
code points
to sequences of values in some fixed-size range, termed
code units
. All UTF encodings map code points to a unique sequence of bytes.
74
The numbers in the names of the encodings indicate the number of bits per code unit (for UTF encodings) or the number of bytes per code unit (for UCS encodings and
UTF-1
). UTF-8 and UTF-16 are the most commonly used encodings.
UCS-2
is an obsolete subset of UTF-16; UCS-4 and UTF-32 are functionally equivalent.
UTF encodings include:
UTF-8
, which uses one to four 8-bit units per
code point
note 3
and has maximal compatibility with
ASCII
UTF-16
, which uses one 16-bit unit per code point below
U+010000
, and a
surrogate pair
of two 16-bit units per code point in the range
U+010000
to
U+10FFFF
UTF-32
, which uses one 32-bit unit per code point
UTF-EBCDIC
, not specified as part of
The Unicode Standard
, which uses one to five 8-bit units per code point, intended to maximize compatibility with
EBCDIC
UTF-8 uses one to four 8-bit units (
bytes
) per code point and, being compact for Latin scripts and ASCII-compatible, provides the de facto standard encoding for the interchange of Unicode text. It is used by
FreeBSD
and most recent
Linux distributions
as a direct replacement for legacy encodings in general text handling.
The UCS-2 and UTF-16 encodings specify the Unicode
byte order mark
(BOM) for use at the beginnings of text files, which may be used for byte-order detection (or
byte endianness
detection). The BOM, encoded as
U+FEFF
ZERO WIDTH NO-BREAK SPACE
, has the important property of unambiguity on byte reorder, regardless of the Unicode encoding used;
U+FFFE
(the result of byte-swapping
U+FEFF
) does not equate to a legal character, and
U+FEFF
in places other than the beginning of text conveys the zero-width non-break space.
The same character converted to UTF-8 becomes the byte sequence
EF BB BF
The Unicode Standard
allows the BOM "can serve as a signature for UTF-8 encoded text where the character set is unmarked".
75
Some software developers have adopted it for other encodings, including UTF-8, in an attempt to distinguish UTF-8 from local 8-bit
code pages
. However
RFC
3629
, the UTF-8 standard, recommends that byte order marks be forbidden in protocols using UTF-8, but discusses the cases where this may not be possible. In addition, the large restriction on possible patterns in UTF-8 (for instance there cannot be any lone bytes with the high bit set) means that it should be possible to distinguish UTF-8 from other character encodings without relying on the BOM.
In UTF-32 and UCS-4, one
32-bit
code unit serves as a fairly direct representation of any character's code point (although the endianness, which varies across different platforms, affects how the code unit manifests as a byte sequence). In the other encodings, each code point may be represented by a variable number of code units. UTF-32 is widely used as an internal representation of text in programs (as opposed to stored or transmitted text), since every Unix operating system that uses the
GCC
compilers to generate software uses it as the standard "
wide character
" encoding. Recent versions of the
Python
programming language (beginning with 2.2) may also be configured to use UTF-32 as the representation for Unicode strings, effectively disseminating such encoding in
high-level
coded software.
Punycode
, another encoding form, enables the encoding of Unicode strings into the limited character set supported by the
ASCII
-based
Domain Name System
(DNS). The encoding is used as part of
IDNA
, which is a system enabling the use of
Internationalized Domain Names
in all scripts that are supported by Unicode. Earlier and now historical proposals include
UTF-5
and
UTF-6
GB18030
is another encoding form for Unicode, from the
Standardization Administration of China
. It is the official
character set
of the People's Republic of China (PRC).
BOCU-1
and
SCSU
are Unicode compression schemes. The
April Fools' Day RFC
of 2005 specified two parody UTF encodings,
UTF-9
and
UTF-18
Adoption
See also:
UTF-8 § Implementations and adoption
Wikibooks has a book on the topic of:
Unicode/Versions
Unicode, in the form of
UTF-8
, has been the most common encoding for the
World Wide Web
since 2008.
76
It has near-universal adoption, and much of the non-UTF-8 content is found in other Unicode encodings, e.g.
UTF-16
. As of 2024
[update]
, UTF-8 accounts for on average 98.3% of all web pages (and 983 of the top 1,000 highest-ranked web pages).
77
Although many pages only use
ASCII
characters to display content, UTF-8 was designed with 8-bit ASCII as a subset and almost no websites now declare their encoding to only be ASCII instead of UTF-8.
78
Over a third of the languages tracked have 100% UTF-8 use.
All internet protocols maintained by
Internet Engineering Task Force
, e.g.
File Transfer Protocol (FTP)
79
have required support for UTF-8 since the publication of
RFC
2277
in 1998, which specified that all IETF protocols "MUST be able to use the UTF-8 charset".
80
Operating systems
Unicode has become the dominant scheme for the internal processing and storage of text. Although a great deal of text is still stored in legacy encodings, Unicode is used almost exclusively for building new information processing systems. Early adopters tended to use
UCS-2
(the fixed-length two-byte obsolete precursor to UTF-16) and later moved to
UTF-16
(the variable-length current standard), as this was the least disruptive way to add support for non-BMP characters. The best known such system is
Windows NT
(and its descendants,
2000
XP
Vista
10
, and
11
), which uses UTF-16 as the sole internal character encoding. The
Java
and
.NET
bytecode environments,
macOS
, and
KDE
also use it for internal representation. Partial support for Unicode can be installed on
Windows 9x
through the Microsoft Layer for Unicode.
UTF-8
(originally developed for
Plan 9
81
has become the main storage encoding on most
Unix-like
operating systems (though others are also used by some libraries) because it is a relatively easy replacement for traditional
extended ASCII
character sets. UTF-8 is also the most common Unicode encoding used in
HTML
documents on the
World Wide Web
Multilingual text-rendering engines which use Unicode include
Uniscribe
and
DirectWrite
for Microsoft Windows,
ATSUI
and
Core Text
for macOS, and
Pango
for
GTK+
and the
GNOME
desktop.
Input methods
Main article:
Unicode input
Because keyboard layouts cannot have simple key combinations for all characters, several operating systems provide alternative input methods that allow access to the entire repertoire.
ISO/IEC 14755
82
which standardises methods for entering Unicode characters from their code points, specifies several methods. There is the
Basic method
, where a
beginning sequence
is followed by the hexadecimal representation of the code point and the
ending sequence
. There is also a
screen-selection entry method
specified, where the characters are listed in a table on a screen, such as with a character map program.
Online tools for finding the code point for a known character include Unicode Lookup
83
by Jonathan Hedley and Shapecatcher
84
by Benjamin Milde. In Unicode Lookup, one enters a search key (e.g. "fractions"), and a list of corresponding characters with their code points is returned. In Shapecatcher, based on
Shape context
, one draws the character in a box and a list of characters approximating the drawing, with their code points, is returned.
Email
Main article:
Unicode and email
MIME
defines two different mechanisms for encoding non-ASCII characters in email, depending on whether the characters are in email headers (such as the "Subject:"), or in the text body of the message; in both cases, the original character set is identified as well as a transfer encoding. For email transmission of Unicode, the
UTF-8
character set and the
Base64
or the
Quoted-printable
transfer encoding are recommended, depending on whether much of the message consists of
ASCII
characters. The details of the two different mechanisms are specified in the MIME standards and generally are hidden from users of email software.
The IETF has defined
85
86
a framework for internationalized email using UTF-8, and has updated
87
88
89
90
several protocols in accordance with that framework.
The adoption of Unicode in email has been very slow.
citation needed
Some East Asian text is still encoded in encodings such as
ISO-2022
, and some devices, such as mobile phones,
citation needed
still cannot correctly handle Unicode data. Support has been improving, however. Many major free mail providers such as
Yahoo! Mail
Gmail
, and
Outlook.com
support it.
Web
Main article:
Unicode and HTML
All
W3C
recommendations have used Unicode as their
document character set
since HTML 4.0.
Web browsers
have supported Unicode, especially UTF-8, for many years. There used to be display problems resulting primarily from
font
related issues; e.g. v6 and older of Microsoft
Internet Explorer
did not render many code points unless explicitly told to use a font that contains them.
91
Although syntax rules may affect the order in which characters are allowed to appear,
XML
(including
XHTML
) documents, by definition,
92
comprise characters from most of the Unicode code points, with the exception of:
FFFE or FFFF.
most of the
C0 control codes
the permanently unassigned code points D800–DFFF,
HTML characters manifest either directly as
bytes
according to the document's encoding, if the encoding supports them, or users may write them as numeric character references based on the character's Unicode code point. For example, the references
Δ
Й
ק
م
๗
あ
叶
葉
, and
말
(or the same numeric values expressed in hexadecimal, with
&#x
as the prefix) should display on all browsers as Δ, Й, ק ,م, ๗, あ, 叶, 葉, and 말.
When specifying
URIs
, for example as
URLs
in
HTTP
requests, non-ASCII characters must be
percent-encoded
Fonts
Main article:
Unicode font
Unicode is not in principle concerned with fonts
per se
, seeing them as implementation choices.
93
Any given character may have many
allographs
, from the more common bold, italic and base letterforms to complex decorative styles. A font is "Unicode compliant" if the glyphs in the font can be accessed using code points defined in
The Unicode Standard
94
The standard does not specify a minimum number of characters that must be included in the font; some fonts have quite a small repertoire.
Free and retail
fonts
based on Unicode are widely available, since
TrueType
and
OpenType
support Unicode (and
Web Open Font Format
(WOFF and
WOFF2
) is based on those). These font formats map Unicode code points to glyphs, but OpenType and TrueType font files are restricted to 65,535 glyphs. Collection files provide a "gap mode" mechanism for overcoming this limit in a single font file. (Each font within the collection still has the 65,535 limit, however.) A TrueType Collection file would typically have a file extension of ".ttc".
Thousands of fonts
exist on the market, but fewer than a dozen fonts—sometimes described as "pan-Unicode" fonts—attempt to support the majority of Unicode's character repertoire. Instead, Unicode-based
fonts
typically focus on supporting only basic ASCII and particular scripts or sets of characters or symbols. Several reasons justify this approach: applications and documents rarely need to render characters from more than one or two writing systems; fonts tend to demand resources in computing environments; and operating systems and applications show increasing intelligence in regard to obtaining glyph information from separate font files as needed, i.e.,
font substitution
. Furthermore, designing a consistent set of rendering instructions for tens of thousands of glyphs constitutes a monumental task; such a venture passes the point of
diminishing returns
for most typefaces.
Newlines
Unicode partially addresses the
newline
problem that occurs when trying to read a text file on different platforms. Unicode defines a large number of
characters
that conforming applications should recognize as line terminators.
In terms of the newline, Unicode introduced
U+2028
LINE SEPARATOR
and
U+2029
PARAGRAPH SEPARATOR
. This was an attempt to provide a Unicode solution to encoding paragraphs and lines semantically, potentially replacing all of the various platform solutions. In doing so, Unicode does provide a way around the historical platform-dependent solutions. Nonetheless, few if any Unicode solutions have adopted these Unicode line and paragraph separators as the sole canonical line ending characters. However, a common approach to solving this issue is through newline normalization. This is achieved with the
Cocoa text system
in
macOS
and also with W3C XML and HTML recommendations. In this approach, every possible newline character is converted internally to a common newline (which one does not really matter since it is an internal operation just for rendering). In other words, the text system can correctly treat the character as a newline, regardless of the input's actual encoding.
Issues
Character unification
Han unification
Main article:
Han unification
The
Ideographic Research Group
(IRG) is tasked with advising the Consortium and ISO regarding Han unification, or Unihan, especially the further addition of CJK unified and compatibility ideographs to the repertoire. The IRG is composed of experts from each region that has historically used
Chinese characters
. However, despite the deliberation within the committee, Han unification has consistently been one of the most contested aspects of
The Unicode Standard
since the genesis of the project.
95
Existing character set standards such as the Japanese
JIS X 0208
(encoded by
Shift JIS
) defined unification criteria, meaning rules for determining when a
variant Chinese character
is to be considered a handwriting/font difference (and thus unified), versus a spelling difference (to be encoded separately). Unicode's character model for CJK characters was based on the unification criteria used by JIS X 0208, as well as those developed by the Association for a Common Chinese Code in China.
96
Due to the standard's principle of encoding semantic instead of stylistic variants, Unicode has received criticism for not assigning code points to certain rare and archaic
kanji
variants, possibly complicating processing of ancient and uncommon Japanese names. Since it places particular emphasis on Chinese, Japanese and Korean sharing many characters in common, Han unification is also sometimes perceived as treating the three as the same thing.
97
Regional differences in the expected forms of characters, in terms of typographical conventions and curricula for handwriting, do not always fall along language boundaries: although
Hong Kong
and
Taiwan
both write
Chinese languages
using
Traditional Chinese
characters, the preferred forms of characters differ between Hong Kong and Taiwan in some cases.
98
Less-frequently-used alternative encodings exist, often predating Unicode, with character models differing from this paradigm, aimed at preserving the various stylistic differences between regional and/or nonstandard character forms. One example is the
TRON Code
favored by some users for handling historical Japanese text, though not widely adopted among the Japanese public. Another is the
CCCII
encoding adopted by library systems in
Hong Kong
Taiwan
and the
United States
. These have their own drawbacks in general use, leading to the
Big5
encoding (introduced in 1984, four years after CCCII) having become more common than CCCII outside of library systems.
99
Although work at
Apple
based on
Research Libraries Group
's CJK Thesaurus, which was used to maintain the EACC variant of CCCII, was one of the direct predecessors of Unicode's
Unihan
set, Unicode adopted the JIS-style unification model.
96
The earliest version of Unicode had a repertoire of fewer than 21,000 Han characters, largely limited to those in relatively common modern usage. As of version 17.0, the standard now encodes more than 101,000 Han characters, and work is continuing to add thousands more—largely historical and dialectal variant characters used throughout the
Sinosphere
Modern typefaces provide a means to address some of the practical issues in depicting unified Han characters with various regional graphical representations. The 'locl'
OpenType
table allows a renderer to select a different glyph for each code point based on the text locale.
100
The
Unicode variation sequences
can also provide in-text annotations for a desired glyph selection; this requires registration of the specific variant in the
Ideographic Variation Database
Italic or cursive characters in Cyrillic
Various
Cyrillic
characters shown with upright, oblique, and italic alternate forms
If the appropriate glyphs for characters in the same script differ only in the italic, Unicode has generally unified them, as can be seen in the comparison among a set of seven characters' italic glyphs as typically appearing in Russian, traditional Bulgarian, Macedonian, and Serbian texts at right, meaning that the differences are displayed through smart font technology or manually changing fonts. The same OpenType 'locl' technique is used.
101
Localised case pairs
For use in the
Turkish alphabet
and
Azeri alphabet
, Unicode includes a separate
dotless lowercase
(ı) and a
dotted uppercase
). However, the usual ASCII letters are used for the lowercase dotted i and the uppercase dotless
, matching how they are handled in the earlier
ISO 8859-9
. As such, case-insensitive comparisons for those languages have to use different rules than case-insensitive comparisons for other languages using the Latin script.
102
103
This can have security implications if, for example,
sanitization
code or
access control
relies on case-insensitive comparison.
103
By contrast, the
Icelandic eth (ð)
, the
barred D (đ)
and the
retroflex D (ɖ)
, which usually
note 4
look the same in uppercase (Đ), are given the opposite treatment, and encoded separately in both letter-cases (in contrast to the earlier
ISO 6937
, which unifies the uppercase forms). Although it allows for case-insensitive comparison without needing to know the language of the text, this approach also has issues, requiring security measures relating to
homoglyph
attacks.
104
Diacritics on lowercase
Localised forms of the letter í (
with
acute accent
Whether the lowercase letter
is expected to retain its
tittle
when a diacritic applies also depends on local conventions.
Security
Unicode has a large number of
homoglyphs
, many of which look very similar or identical to ASCII letters. Substitution of these can make an identifier or URL that looks correct, but directs to a different location than expected.
105
Additionally, homoglyphs can also be used for manipulating the output of
natural language processing (NLP)
systems.
106
Mitigation requires disallowing these characters, displaying them differently, or requiring that they resolve to the same identifier;
107
all of this is complicated due to the huge and constantly changing set of characters.
108
109
A security advisory was released in 2021 by two researchers, one from the
University of Cambridge
and the other from the
University of Edinburgh
, in which they assert that the
BiDi marks
can be used to make large sections of code do something different from what they appear to do. The problem was named "
Trojan Source
".
110
In response, code editors started highlighting marks to indicate forced text-direction changes.
111
The
UTF-8
and
UTF-16
encodings do not accept all possible sequences of code units. Implementations vary in what they do when reading an invalid sequence, which has led to security bugs.
112
113
Mapping to legacy character sets
Unicode was designed to provide code-point-by-code-point
round-trip format conversion
to and from any preexisting character encodings, so that text files in older character sets can be converted to Unicode and then back and get back the same file, without employing context-dependent interpretation. That has meant that inconsistent legacy architectures, such as
combining diacritics
and
precomposed characters
, both exist in Unicode, giving more than one method of representing some text. This is most pronounced in the three different encoding forms for Korean
Hangul
. Since version 3.0, any precomposed characters that can be represented by a combined sequence of already existing characters can no longer be added to the standard to preserve interoperability between software using different versions of Unicode.
Injective
mappings must be provided between characters in existing legacy character sets and characters in Unicode to facilitate conversion to Unicode and allow interoperability with legacy software. Lack of consistency in various mappings between earlier Japanese encodings such as
Shift-JIS
or
EUC-JP
and Unicode led to
round-trip format conversion
mismatches, particularly the mapping of the character JIS X 0208 '～' (1-33, WAVE DASH), heavily used in legacy database data, to either
U+FF5E
FULLWIDTH TILDE
(in
Microsoft Windows
) or
U+301C
WAVE DASH
(other vendors).
114
Some Japanese computer programmers objected to Unicode because it requires them to separate the use of
U+005C
REVERSE SOLIDUS
(backslash) and
U+00A5
YEN SIGN
, which was mapped to 0x5C in JIS X 0201, and a lot of legacy code exists with this usage.
115
(This encoding also replaces tilde '~' 0x7E with macron '¯', now 0xAF.) The separation of these characters exists in
ISO 8859-1
, from long before Unicode.
Indic scripts
Further information:
Tamil All Character Encoding
Indic scripts
such as
Tamil
and
Devanagari
are each allocated only 128 code points, matching the
ISCII
standard. The correct rendering of Unicode Indic text requires transforming the stored logical order characters into visual order and the forming of ligatures (also known as conjuncts) out of components. Some local scholars argued in favor of assignments of Unicode code points to these ligatures, going against the practice for other writing systems, though Unicode contains some Arabic and other ligatures for backward compatibility purposes only.
116
117
118
Encoding of any new ligatures in Unicode will not happen, in part, because the set of ligatures is font-dependent, and Unicode is an encoding independent of font variations. The same kind of issue arose for the
Tibetan script
in 2003 when the
Standardization Administration of China
proposed encoding 956 precomposed Tibetan syllables,
119
but these were rejected for encoding by the relevant ISO committee (
ISO/IEC JTC 1/SC 2
).
120
Thai alphabet
support has been criticized for its ordering of Thai characters. The vowels เ, แ, โ, ใ, ไ that are written to the left of the preceding consonant are in visual order instead of phonetic order, unlike the Unicode representations of other Indic scripts. This complication is due to Unicode inheriting the
Thai Industrial Standard 620
, which worked in the same way, and was the way in which Thai had always been written on keyboards. This ordering problem complicates the Unicode collation process slightly, requiring table lookups to reorder Thai characters for collation.
97
Even if Unicode had adopted encoding according to spoken order, it would still be problematic to collate words in dictionary order. E.g., the word
แสดง
[sa
dɛːŋ]
"perform" starts with a consonant cluster "สด" (with an inherent vowel for the consonant "ส"), the vowel แ-, in spoken order would come after the ด, but in a dictionary, the word is collated as it is written, with the vowel following the ส.
Combining characters
Main article:
Combining character
See also:
Unicode normalization § Normalization
Characters with diacritical marks can generally be represented either as a single precomposed character or as a decomposed sequence of a base letter plus one or more non-spacing marks. For example, ḗ (precomposed e with macron and acute above) and ḗ (e followed by the combining macron above and combining acute above) should be rendered identically, both appearing as an
with a
macron
(◌̄) and
acute accent
(◌́), but in practice, their appearance may vary depending upon what rendering engine and fonts are being used to display the characters. Similarly,
underdots
, as needed in the
romanization
of
Indic languages
, will often be placed incorrectly.
citation needed
Unicode characters that map to precomposed glyphs can be used in many cases, thus avoiding the problem, but where no precomposed character has been encoded, the problem can often be solved by using a specialist Unicode font such as
Charis SIL
that uses
Graphite
OpenType
('gsub'), or
AAT
technologies for advanced rendering features.
Anomalies
Main article:
Unicode alias names and abbreviations
The Unicode Standard
has imposed rules intended to guarantee stability.
121
Depending on the strictness of a rule, a change can be prohibited or allowed. For example, a "name" given to a code point cannot and will not change. But a "script" property is more flexible, by Unicode's own rules. In version 2.0, Unicode changed many code point "names" from version 1. At the same moment, Unicode stated that, thenceforth, an assigned name to a code point would never change. This implies that when mistakes are published, these mistakes cannot be corrected, even if they are trivial (as happened in one instance with the spelling
BRAKCET
for
BRACKET
in a character name). In 2006 a list of anomalies in character names was first published, and, as of June 2021, there were 104 characters with identified issues,
122
for example:
U+034F
COMBINING GRAPHEME JOINER
: Does not join graphemes.
122
U+2118
SCRIPT CAPITAL P
: This is a small letter. The capital is
U+1D4AB
MATHEMATICAL SCRIPT CAPITAL P
123
U+A015
YI SYLLABLE WU
: This is not a Yi syllable, but a Yi iteration mark.
U+FE18
PRESENTATION FORM FOR VERTICAL RIGHT WHITE LENTICULAR BRAKCET
bracket
is spelled incorrectly.
124
(Spelling errors are resolved by using
Unicode alias names
.)
While Unicode defines the script designator (name) to be "
Phags_Pa
", in that script's character names, a hyphen is added:
U+A840
PHAGS-PA LETTER KA
125
126
This, however, is not an anomaly, but the rule: hyphens are replaced by underscores in script designators.
125
See also
Comparison of Unicode encodings
International Components for Unicode
(ICU), now as ICU-
TC
a part of Unicode
List of binary codes
List of Unicode characters
List of XML and HTML character entity references
Lotus Multi-Byte Character Set
(LMBCS), a parallel development with similar intentions
Open-source Unicode typefaces
Religious and political symbols in Unicode
Standards related to Unicode
Unicode symbol
Universal Coded Character Set
Notes
"A Unicode Standard Annex (UAX) forms an integral part of
The Unicode Standard
, but is published as a separate document."
[1]
The two-character prefix
U+
was chosen as an ASCII approximation of
U+228E
MULTISET UNION
62
code point
is an abstract representation of an UCS character by an integer between 0 and 1,114,111 (1,114,112 = 2
20
+ 2
16
or 17 × 2
16
= 0x110000 code points)
Rarely, the uppercase Icelandic eth may instead be written in an
insular
style (Ꝺ) with the crossbar positioned on the stem, particularly if it needs to be distinguished from the uppercase retroflex D (see
African Reference Alphabet
).
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Archived
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Overview and Framework for Internationalized Email
IETF
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10.17487/RFC4952
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2022-08-17
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Overview and Framework for Internationalized Email
IETF
doi
10.17487/RFC6530
RFC
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2022-08-17
J. Yao; W. Mao (February 2012).
SMTP Extension for Internationalized Email
IETF
doi
10.17487/RFC6531
RFC
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2022-08-17
A. Yang; S. Steele; N. Freed (February 2012).
Internationalized Email Headers
IETF
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C. Newman; A. Gulbrandsen; A. Melnikov (June 2008).
Internet Message Access Protocol Internationalization
IETF
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2022-08-17
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POP3 Support for UTF-8
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Wood, Alan (2005-09-13).
"Setting up Windows Internet Explorer 5, 5.5 and 6 for Multilingual and Unicode Support:
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"Extensible Markup Language (XML) 1.1 (Second Edition)"
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Archived
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Bigelow, Charles; Holmes, Kris (September 1993).
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ISSN
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Archived
(PDF)
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2025-04-12
"FAQs: Fonts and keyboards:
Fonts and Unicode
Unicode Consortium
Archived
from the original on 2025-03-06
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2025-04-12
A Brief History of Character Codes
, Steven J. Searle, originally written
1999
, last updated 2004
"Appendix E: Han Unification History"
The Unicode Standard Version 16.0 – Core Specification
Unicode Consortium
. 2024.
Topping, Suzanne (2013-06-25).
"The secret life of Unicode"
IBM
. Archived from
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2023-03-20
Lu, Qin (2015-06-08).
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ISO/IEC JTC1
SC2
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"Chinese character codes: an update"
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"Noto CJK fonts"
. Noto Fonts. 2023-02-18.
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Preuss, Ingo.
"OpenType Feature: locl – Localized Forms"
preusstype.com
"Case Folding Properties"
Unicode Character Database
Unicode Consortium
. 2025-07-30.
"Regular expression options § Compare using the invariant culture"
.NET
fundamentals documentation
Microsoft
. 2023-05-12.
"confusablesSummary.txt"
Unicode Security Mechanisms for UTS #39
Unicode Consortium
. 2023-08-11.
"UTR #36: Unicode Security Considerations"
Unicode
Boucher, Nicholas; Shumailov, Ilia; Anderson, Ross; Papernot, Nicolas (2022). "Bad Characters: Imperceptible NLP Attacks".
2022 IEEE Symposium on Security and Privacy (SP)
. San Francisco, CA, US: IEEE. pp.
1987–
2004.
arXiv
2106.09898
doi
10.1109/SP46214.2022.9833641
ISBN
978-1-66541-316-9
S2CID
235485405
Engineering, Spotify (2013-06-18).
"Creative usernames and Spotify account hijacking"
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Wheeler, David A. (2020).
Initial Analysis of Underhanded Source Code
(Technical report). p. 4–1–4–10.
JSTOR
resrep25332.7
"UTR #36: Unicode Security Considerations"
Unicode
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2022-06-27
Boucher, Nicholas; Anderson, Ross.
"Trojan Source: Invisible Vulnerabilities"
(PDF)
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2021-11-02
"Visual Studio Code October 2021"
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2021-11-11
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Boone, Kevin.
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2024-12-26
AFII contribution about WAVE DASH
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2019-05-20
ISO 646-* Problem
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"Arabic Presentation Forms-A"
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2010-03-20
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2010-03-20
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"Unicode Technical Note #27: Known Anomalies in Unicode Character Names"
Unicode
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"Unicode chart: "actually this has the form of a lowercase calligraphic p, despite its name"
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Further reading
Julie D. Allen.
The Unicode Standard, Version 6.0
, The
Unicode Consortium
, Mountain View, 2011,
ISBN
9781936213016
, (
Unicode 6.0.0
).
The Complete Manual of Typography
, James Felici, Adobe Press; 1st edition, 2002.
ISBN
0-321-12730-7
The Unicode Standard, Version 3.0
, The Unicode Consortium, Addison-Wesley Longman, Inc., April 2000.
ISBN
0-201-61633-5
The Unicode Standard, Version 4.0
, The Unicode Consortium, Addison-Wesley Professional, 27 August 2003.
ISBN
0-321-18578-1
The Unicode Standard, Version 5.0, Fifth Edition
, The
Unicode Consortium
, Addison-Wesley Professional, 27 October 2006.
ISBN
0-321-48091-0
Unicode Demystified: A Practical Programmer's Guide to the Encoding Standard
, Richard Gillam, Addison-Wesley Professional; 1st edition, 2002.
ISBN
0-201-70052-2
Unicode Explained
, Jukka K. Korpela, O'Reilly; 1st edition, 2006.
ISBN
0-596-10121-X
Unicode: A Primer
, Tony Graham, M&T books, 2000.
ISBN
0-7645-4625-2
Haralambous, Yannis; Martin Dürst (2019). "Unicode from a Linguistic Point of View". In Haralambous, Yannis (ed.).
Proceedings of Graphemics in the 21st Century, Brest 2018
. Brest: Fluxus Editions. pp.
167–
183.
doi
10.36824/2018-graf-hara1
ISBN
978-2-9570549-1-6
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