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Alias(es) Universal Coded Character Set (UCS, ISO/IEC 10646)
StandardUnicode Standard
Encoding formats
Preceded by ISO/IEC 8859, various others

Unicode, formally The Unicode Standard, [note 1] [note 2] is an information technology standard for the consistent encoding, representation, and handling of text expressed in most of the world's writing systems. The standard, which is maintained by the Unicode Consortium, defines as of the current version (15.0) 149,186 characters [3] [4] covering 161 modern and historic scripts, as well as symbols, emoji (including in colors), and non-visual control and formatting codes.


Unicode's success at unifying character sets has led to its widespread and predominant use in the internationalization and localization of computer software. The standard has been implemented in many recent technologies, including modern operating systems, XML, and most modern programming languages.

The Unicode character repertoire is synchronized with ISO/IEC 10646, each being code-for-code identical with the other. The Unicode Standard, however, includes more than just the base code. Alongside the character encodings, the Consortium's official publication includes a wide variety of details about the scripts and how to display them: normalization rules, decomposition, collation, rendering, and bidirectional text display order for multilingual texts, and so on. [5] The Standard also includes reference data files and visual charts to help developers and designers correctly implement the repertoire.

Unicode can be stored using several different encodings, which translate the character codes into sequences of bytes. The Unicode standard defines three and several other encodings exist, all in practice variable-length encodings. The most common encodings are the ASCII-compatible UTF-8, the ASCII-incompatible UTF-16 (compatible with the obsolete UCS-2), and the Chinese Unicode encoding standard GB18030 which is not an official Unicode standard but is used in China and implements Unicode fully.

Origin and development

Unicode has the explicit aim of transcending the limitations of traditional character encodings, such as those defined by the ISO/IEC 8859 standard, which find wide usage in various countries of the world but remain largely incompatible with each other. Many traditional character encodings share a common problem in that they allow bilingual computer processing (usually using Latin characters and the local script), but not multilingual computer processing (computer processing of arbitrary scripts mixed with each other).

Unicode, in intent, encodes the underlying characters—graphemes and grapheme-like units—rather than the variant glyphs (renderings) for such characters. In the case of Chinese characters, this sometimes leads to controversies over distinguishing the underlying character from its variant glyphs (see Han unification).

In text processing, Unicode takes the role of providing a unique code point—a number, not a glyph—for each character. In other words, Unicode represents a character in an abstract way and leaves the visual rendering (size, shape, font, or style) to other software, such as a web browser or word processor. This simple aim becomes complicated, however, because of concessions made by Unicode's designers in the hope of encouraging a more rapid adoption of Unicode.

The first 256 code points were made identical to the content of ISO/IEC 8859-1 so as to make it trivial to convert existing western text. Many essentially identical characters were encoded multiple times at different code points to preserve distinctions used by legacy encodings and therefore, allow conversion from those encodings to Unicode (and back) without losing any information. For example, the "fullwidth forms" section of code points encompasses a full duplicate of the Latin alphabet because Chinese, Japanese, and Korean (CJK) fonts contain two versions of these letters, "fullwidth" matching the width of the CJK characters, and normal width. For other examples, see duplicate characters in Unicode.

Unicode Bulldog Award recipients include many names influential in the development of Unicode and include Tatsuo Kobayashi, Thomas Milo, Roozbeh Pournader, Ken Lunde, and Michael Everson. [6]


Based on experiences with the Xerox Character Code Standard (XCCS) since 1980, [7] the origins of Unicode can be traced back to 1987, when Joe Becker from Xerox with Lee Collins and Mark Davis from Apple started investigating the practicalities of creating a universal character set. [8] With additional input from Peter Fenwick and Dave Opstad, [7] Joe 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". [7]

In this document, entitled Unicode 88, Becker outlined a 16-bit character model: [7]

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.

His original 16-bit design was based on the assumption that only those scripts and characters in modern use would need to be encoded: [7]

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 modern text (e.g. in the union of all newspapers and magazines printed in the world in 1988), whose number is undoubtedly far below 214 = 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 Unicodes.

In early 1989, the Unicode working group expanded to include Ken Whistler and Mike Kernaghan of Metaphor, Karen Smith-Yoshimura and Joan Aliprand of RLG, and Glenn Wright of Sun Microsystems, and in 1990, Michel Suignard and Asmus Freytag from Microsoft and Rick McGowan of NeXT joined the group. By the end of 1990, most of the work on mapping existing character encoding standards had been completed, and a final review draft of Unicode was ready.

The Unicode Consortium was incorporated in California on 3 January 1991, [9] and in October 1991, the first volume of the Unicode standard was published. The second volume, covering 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 (e.g., Egyptian hieroglyphs) and thousands of rarely used or obsolete characters that had not been anticipated as needing encoding. Among the characters not originally intended for Unicode are rarely used Kanji or Chinese characters, many of which are part of personal and place names, making them much more essential than envisioned in the original architecture of Unicode. [10]

The Microsoft TrueType specification version 1.0 from 1992 used the name 'Apple Unicode' instead of 'Unicode' for the Platform ID in the naming table.

Unicode Consortium

The Unicode Consortium is a nonprofit organization that coordinates Unicode's development. Full members include most of the main computer software and hardware companies with any interest in text-processing standards, including Adobe, Apple, Facebook, Google, IBM, Microsoft, Netflix, and SAP SE. [11]

Over the years several countries or government agencies have been members of the Unicode Consortium. Presently only the Ministry of Endowments and Religious Affairs (Oman) is a full member with voting rights. [11]

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.

Scripts covered

Many modern applications can render a substantial subset of the many scripts in Unicode, as demonstrated by this screenshot from the OpenOffice.org application. Unicode sample.png
Many modern applications can render a substantial subset of the many scripts in Unicode, as demonstrated by this screenshot from the OpenOffice.org application.

Unicode currently covers most major writing systems in use today. [12] [ better source needed ]

As of 2022, a total of 161 scripts [13] are included in the latest version of Unicode (covering alphabets, abugidas and syllabaries), although 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 (in the form of notes and rhythmic symbols), also occur.

The Unicode Roadmap Committee (Michael Everson, Rick McGowan, Ken Whistler, V.S. Umamaheswaran) [14] maintain the list of scripts that are candidates or potential candidates for encoding and their tentative code block assignments on the Unicode Roadmap [15] page of the Unicode Consortium website. For some scripts on the Roadmap, such as Jurchen and Khitan small script, encoding proposals have been made and they are working their way through the approval process. For other scripts, such as Mayan (besides numbers) 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 Areas code assignments.

There is also a Medieval Unicode Font Initiative focused on special Latin medieval characters. Part of these proposals have been already included into Unicode.

Script Encoding Initiative

The Script Encoding Initiative, [16] a project run 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. The project has become a major source of proposed additions to the standard in recent years. [17]


The Unicode Consortium and the International Organization for Standardization (ISO) have together developed a shared repertoire following the initial publication of The Unicode Standard in 1991; 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, and code charts. However, Unicode 5.0, published in 2006, was the last version printed this way. Starting with version 5.2, only the core specification, published as print-on-demand paperback, may be purchased. [18] 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, only 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 from March 2021 to September 2021 due to the COVID-19 pandemic.

The latest version of Unicode, 15.0.0, was released on 13 September 2022. Several annexes were updated including Unicode Security Mechanisms (UTS #39), and a total of 4489 new characters were encoded, including 20 new emoji characters, such as "wireless" (network) symbol and hearts in different colors such as pink, two new scripts, CJK Unified Ideographs extension, and multiple additions to existing blocks. [19] [20]

Thus far, the following major and minor 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]

VersionDateBookCorresponding ISO/IEC 10646 edition Scripts Characters
Total [tablenote 1] Notable additions
1.0.0 [22] October 1991 ISBN   0-201-56788-1 (Vol. 1)247,129 [tablenote 2] Initial repertoire covers these scripts: Arabic, Armenian, Bengali, Bopomofo, Cyrillic, Devanagari, Georgian, Greek and Coptic, Gujarati, Gurmukhi, Hangul, Hebrew, Hiragana, Kannada, Katakana, Lao, Latin, Malayalam, Oriya, Tamil, Telugu, Thai, and Tibetan. [22]
1.0.1 [23] June 1992ISBN  0-201-60845-6 (Vol. 2)2528,327
(21,204 added;
6 removed)
The initial set of 20,902 CJK Unified Ideographs is defined. [23]
1.1 [24] June 1993 ISO/IEC 10646-1:19932434,168
(5,963 added;
89 removed;
33 reclassified
as control
4,306 more Hangul syllables added to original set of 2,350 characters. Tibetan removed. [24]
2.0 [25] July 1996ISBN  0-201-48345-9 ISO/IEC 10646-1:1993 plus Amendments 5, 6 and 72538,885
(11,373 added;
6,656 removed)
Original set of Hangul syllables removed, and a new set of 11,172 Hangul syllables added at a new location. Tibetan added back in a new location and with a different character repertoire. Surrogate character mechanism defined, and Plane 15 and Plane 16 Private Use Areas allocated. [25]
2.1 [26] May 1998ISO/IEC 10646-1:1993 plus Amendments 5, 6 and 7, as well as two characters from Amendment 182538,887
(2 added)
Euro sign and Object Replacement Character added. [26]
3.0September 1999ISBN  0-201-61633-5 ISO/IEC 10646-1:20003849,194
(10,307 added)
Cherokee, Ethiopic, Khmer, Mongolian, Burmese, Ogham, Runic, Sinhala, Syriac, Thaana, Unified Canadian Aboriginal Syllabics, and Yi Syllables added, as well as a set of Braille patterns. [27]
3.1March 2001ISO/IEC 10646-1:2000

ISO/IEC 10646-2:2001

(44,946 added)
Deseret, Gothic and Old Italic added, as well as sets of symbols for Western music and Byzantine music, and 42,711 additional CJK Unified Ideographs. [28]
3.2March 2002ISO/IEC 10646-1:2000 plus Amendment 1

ISO/IEC 10646-2:2001

(1,016 added)
Philippine scripts Buhid, Hanunó'o, Tagalog, and Tagbanwa added. [29]
4.0April 2003ISBN  0-321-18578-1 ISO/IEC 10646:20035296,382
(1,226 added)
Cypriot syllabary, Limbu, Linear B, Osmanya, Shavian, Tai Le, and Ugaritic added, as well as Hexagram symbols. [30]
4.1March 2005ISO/IEC 10646:2003 plus Amendment 15997,655
(1,273 added)
Buginese, Glagolitic, Kharoshthi, New Tai Lue, Old Persian, Syloti Nagri, and Tifinagh added, and Coptic was disunified from Greek. Ancient Greek numbers and musical symbols were also added. [31]
5.0July 2006ISBN  0-321-48091-0 ISO/IEC 10646:2003 plus Amendments 1 and 2, as well as four characters from Amendment 36499,024
(1,369 added)
Balinese, Cuneiform, N'Ko, Phags-pa, and Phoenician added. [32]
5.1April 2008ISO/IEC 10646:2003 plus Amendments 1, 2, 3 and 475100,648
(1,624 added)
Carian, Cham, Kayah Li, Lepcha, Lycian, Lydian, Ol Chiki, Rejang, Saurashtra, Sundanese, and Vai added, as well as sets of symbols for the Phaistos Disc, Mahjong tiles, and Domino tiles. There were also important additions for Burmese, additions of letters and Scribal abbreviations used in medieval manuscripts, and the addition of Capital ẞ. [33]
5.2October 2009ISBN  978-1-936213-00-9 ISO/IEC 10646:2003 plus Amendments 1, 2, 3, 4, 5 and 690107,296
(6,648 added)
Avestan, Bamum, Egyptian hieroglyphs (the Gardiner Set, comprising 1,071 characters), Imperial Aramaic, Inscriptional Pahlavi, Inscriptional Parthian, Javanese, Kaithi, Lisu, Meetei Mayek, Old South Arabian, Old Turkic, Samaritan, Tai Tham and Tai Viet added. 4,149 additional CJK Unified Ideographs (CJK-C), as well as extended Jamo for Old Hangul, and characters for Vedic Sanskrit. [34]
6.0October 2010ISBN  978-1-936213-01-6 ISO/IEC 10646:2010 plus the Indian rupee sign 93109,384
(2,088 added)
Batak, Brahmi, Mandaic, playing card symbols, transport and map symbols, alchemical symbols, emoticons and emojis. [35] 222 additional CJK Unified Ideographs (CJK-D) added. [36]
6.1January 2012ISBN  978-1-936213-02-3 ISO/IEC 10646:2012100110,116
(732 added)
Chakma, Meroitic cursive, Meroitic hieroglyphs, Miao, Sharada, Sora Sompeng, and Takri. [37]
6.2September 2012ISBN  978-1-936213-07-8 ISO/IEC 10646:2012 plus the Turkish lira sign 100110,117
(1 added)
Turkish lira sign. [38]
6.3September 2013ISBN  978-1-936213-08-5 ISO/IEC 10646:2012 plus six characters100110,122
(5 added)
5 bidirectional formatting characters. [39]
7.0June 2014ISBN  978-1-936213-09-2 ISO/IEC 10646:2012 plus Amendments 1 and 2, as well as the Ruble sign 123112,956
(2,834 added)
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. [40]
8.0June 2015ISBN  978-1-936213-10-8 ISO/IEC 10646:2014 plus Amendment 1, as well as the Lari sign, nine CJK unified ideographs, and 41 emoji characters [41] 129120,672
(7,716 added)
Ahom, Anatolian hieroglyphs, Hatran, Multani, Old Hungarian, SignWriting, 5,771 CJK Unified Ideographs, a set of lowercase letters for Cherokee, and five emoji skin tone modifiers. [42]
9.0June 2016ISBN  978-1-936213-13-9 ISO/IEC 10646:2014 plus Amendments 1 and 2, as well as Adlam, Newa, Japanese TV symbols, and 74 emoji and symbols [43] 135128,172
(7,500 added)
Adlam, Bhaiksuki, Marchen, Newa, Osage, Tangut, and 72 emoji. [44] [45]
10.0June 2017ISBN  978-1-936213-16-0 ISO/IEC 10646:2017 plus 56 emoji characters, 285 hentaigana characters, and 3 Zanabazar Square characters [46] 139136,690
(8,518 added)
Zanabazar Square, Soyombo, Masaram Gondi, Nüshu, hentaigana (non-standard hiragana), 7,494 CJK Unified Ideographs, 56 emoji, and bitcoin symbol. [47]
11.0June 2018ISBN  978-1-936213-19-1 ISO/IEC 10646:2017 plus Amendment 1, as well as 46 Mtavruli Georgian capital letters, 5 CJK unified ideographs, and 66 emoji characters. [48] 146137,374
(684 added)
Dogra, Georgian Mtavruli capital letters, Gunjala Gondi, Hanifi Rohingya, Indic Siyaq Numbers, Makasar, Medefaidrin, Old Sogdian and Sogdian, Mayan numerals, 5 urgently needed CJK Unified Ideographs, symbols for xiangqi (Chinese chess) and star ratings, and 145 emoji. [49]
12.0March 2019ISBN  978-1-936213-22-1 ISO/IEC 10646:2017 plus Amendments 1 and 2, as well as 62 additional characters. [50] 150137,928
(554 added)
Elymaic, Nandinagari, Nyiakeng Puachue Hmong, Wancho, Miao script additions for several Miao and Yi languages of China, hiragana and katakana small letters for writing archaic Japanese, Tamil historic fractions and symbols, Lao letters for Pali, Latin letters for Egyptological and Ugaritic transliteration, hieroglyph format controls, and 61 emoji. [51]
12.1May 2019ISBN  978-1-936213-25-2 150137,929
(1 added)
Adds a single character at U+32FF for the square ligature form of the name of the Reiwa era. [52]
13.0 [53] March 2020ISBN  978-1-936213-26-9 ISO/IEC 10646:2020 [54] 154143,859
(5,930 added)
Chorasmian, Dives Akuru, Khitan small script, Yezidi, 4,969 CJK unified ideographs added (including 4,939 in Ext. G), Arabic script additions used to write Hausa, Wolof, and other languages in Africa and other 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 from the 1970s and 1980s, and 55 emoji. [53]
14.0 [55] September 2021ISBN  978-1-936213-29-0 159144,697
(838 added)
Toto, Cypro-Minoan, Vithkuqi, Old Uyghur, Tangsa, Latin script additions at SMP blocks (Ext-F, Ext-G) for use in extended IPA, Arabic script additions for use in languages across Africa and in Iran, Pakistan, Malaysia, Indonesia, Java, and Bosnia, and to write honorifics, additions for Quranic use, other additions to support languages in North America, the Philippines, India, and Mongolia, addition of the Kyrgyzstani som currency symbol, support for Znamenny musical notation, and 37 emoji. [55]
15.0 [56] September 2022ISBN  978-1-936213-32-0 161149,186
(4,489 added)
Kawi and Mundari, several new characters, including 20 emoji, 4,192 CJK ideographs, and control characters for Egyptian hieroglyphs. [56]
  1. The number of characters listed for each version of Unicode is the total number of graphic and format characters (i.e., excluding private-use characters, control characters, noncharacters and surrogate code points).
  2. Not counting 'space' or 33 non-printing characters (7,163 total) [22]

Architecture and terminology

Codespace and Code Points

The Unicode Standard defines a codespace, [57] a set of numerical values ranging from 0 through 10FFFF 16 , [58] called code points [59] and denoted as U+0000 through U+10FFFF ("U+" [60] followed by the code point value in hexadecimal, which is prepended with leading zeros to a minimum of four digits; e. g., U+00F7 for the division sign ÷ but U+13254 (notU+013254) for the Egyptian hieroglyph Hiero O4.png . [61] ). Of these 216 + 220 defined code points, the code points from U+D800 through U+DFFF, which are used to encode surrogate pairs in UTF-16, are reserved by the Unicode Standard and may not be used to encode valid characters, resulting in a net total of 216 211 + 220 = 1,112,064 assignable code points.

Code planes and blocks

The Unicode codespace is divided into seventeen planes, numbered 0 to 16. Plane 0 is the Basic Multilingual Plane (BMP), which contains 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 (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. Although blocks are an arbitrary size, they are always a multiple of 16 code points and often a multiple of 128 code points. Characters required for a given script may be spread out over several different blocks.

General Category property

Each code point has a single General Category property. The major categories are denoted: Letter, Mark, Number, Punctuation, Symbol, Separator and Other. Within these categories, there are subdivisions. In most cases other properties must be used to sufficiently specify the characteristics of a code point. The possible General Categories are:

General Category (Unicode Character Property) [lower-alpha 1]
ValueCategory Major, minorBasic type [lower-alpha 2] Character assigned [lower-alpha 2] Count [lower-alpha 3]
(as of 15.0)
L, Letter; LC, Cased Letter (Lu, Ll, and Lt only) [lower-alpha 4]
LuLetter, uppercaseGraphicCharacter1,831
LlLetter, lowercaseGraphicCharacter2,233
LtLetter, titlecaseGraphicCharacter31 Ligatures containing uppercase followed by lowercase letters (e.g., Dž, Lj, Nj, and Dz)
LmLetter, modifierGraphicCharacter397A modifier letter
LoLetter, otherGraphicCharacter131,612An ideograph or a letter in a unicase alphabet
M, Mark
MnMark, nonspacingGraphicCharacter1,985
McMark, spacing combiningGraphicCharacter452
MeMark, enclosingGraphicCharacter13
N, Number
NdNumber, decimal digitGraphicCharacter680All these, and only these, have Numeric Type = De [lower-alpha 5]
NlNumber, letterGraphicCharacter236Numerals composed of letters or letterlike symbols (e.g., Roman numerals)
NoNumber, otherGraphicCharacter915E.g., vulgar fractions, superscript and subscript digits
P, Punctuation
PcPunctuation, connectorGraphicCharacter10Includes 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. [lower-alpha 6]
PdPunctuation, dashGraphicCharacter26Includes several hyphen characters
PsPunctuation, openGraphicCharacter79Opening bracket characters
PePunctuation, closeGraphicCharacter77Closing bracket characters
PiPunctuation, initial quoteGraphicCharacter12Opening quotation mark. Does not include the ASCII "neutral" quotation mark. May behave like Ps or Pe depending on usage
PfPunctuation, final quoteGraphicCharacter10Closing quotation mark. May behave like Ps or Pe depending on usage
PoPunctuation, otherGraphicCharacter628
S, Symbol
SmSymbol, mathGraphicCharacter948 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".
ScSymbol, currencyGraphicCharacter63 Currency symbols
SkSymbol, modifierGraphicCharacter125
SoSymbol, otherGraphicCharacter6,634
Z, Separator
ZsSeparator, spaceGraphicCharacter17Includes the space, but not TAB, CR, or LF, which are Cc
ZlSeparator, lineFormatCharacter1Only U+2028LINE SEPARATOR (LSEP)
ZpSeparator, paragraphFormatCharacter1Only U+2029PARAGRAPH SEPARATOR (PSEP)
C, Other
CcOther, controlControlCharacter65 (will never change) [lower-alpha 5] No name, [lower-alpha 7] <control>
CfOther, formatFormatCharacter170Includes the soft hyphen, joining control characters (ZWNJ and ZWJ), control characters to support bidirectional text, and language tag characters
CsOther, surrogateSurrogateNot (only used in UTF-16)2,048 (will never change) [lower-alpha 5] No name, [lower-alpha 7] <surrogate>
CoOther, private usePrivate-useCharacter (but no interpretation specified)137,468 total (will never change) [lower-alpha 5] (6,400 in BMP , 131,068 in Planes 1516 )No name, [lower-alpha 7] <private-use>
CnOther, not assignedNoncharacterNot66 (will never change) [lower-alpha 5] No name, [lower-alpha 7] <noncharacter>
ReservedNot825,279No name, [lower-alpha 7] <reserved>
  1. "Table 4-4: General Category" (PDF). The Unicode Standard. Unicode Consortium. September 2022.
  2. 1 2 "Table 2-3: Types of code points" (PDF). The Unicode Standard. Unicode Consortium. September 2022.
  3. "DerivedGeneralCategory.txt". The Unicode Consortium. 2022-04-26.
  4. "5.7.1 General Category Values". UTR #44: Unicode Character Database. Unicode Consortium. 2020-03-04.
  5. 1 2 3 4 5 Unicode Character Encoding Stability Policies: Property Value Stability Stability policy: Some gc groups will never change. gc=Nd corresponds with Numeric Type=De (decimal).
  6. "Annex C: Compatibility Properties (§ word)". Unicode Regular Expressions. Version 23. Unicode Consortium. 2022-02-08. Unicode Technical Standard #18.
  7. 1 2 3 4 5 "Table 4-9: Construction of Code Point Labels" (PDF). The Unicode Standard. Unicode Consortium. September 2022. A Code Point Label may be used to identify a nameless code point. E.g. <control-hhhh>, <control-0088>. The Name remains blank, which can prevent inadvertently replacing, in documentation, a Control Name with a true Control code. Unicode also uses <not a character> for <noncharacter>.

Code points in the range U+D800–U+DBFF (1,024 code points) are known as high-surrogate code points, and code points in the range U+DC00–U+DFFF (1,024 code points) are known as low-surrogate code points. A high-surrogate code point followed by a low-surrogate code point form a surrogate pair in UTF-16 to represent code points greater than U+FFFF. These code points otherwise cannot be used (this rule is ignored often in practice especially when not using UTF-16).

A small set of code points are guaranteed never to be used for encoding characters, although applications may make use of these code points internally if they wish. There are sixty-six of these noncharacters: U+FDD0–U+FDEF and any code point ending in the value FFFE or FFFF (i.e., 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. [62] Like surrogates, the rule that these cannot be used is often ignored, although the operation of the byte order mark (BOM) assumes that U+FFFE will never be the first code point in a text.

Excluding surrogates and noncharacters leaves 1,111,998 code points available for use.

Private-use code points are considered to be assigned characters, but they have no interpretation specified by the Unicode standard [63] so any interchange of such characters requires an agreement between sender and receiver on their interpretation. There are three private-use areas in the Unicode codespace:

Graphic characters are characters defined by Unicode to have particular semantics, and either have a visible glyph shape or represent a visible space. As of Unicode 15.0 there are 149,014 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 15.0.

Sixty-five code points (U+0000–U+001F and U+007F–U+009F) are reserved as control codes, and correspond to the C0 and C1 control codes defined in ISO/IEC 6429. U+0009 (Tab), U+000A (Line Feed), and U+000D (Carriage Return) are widely used in Unicode-encoded texts. In practice the C1 code points are often improperly-translated (mojibake) as the legacy Windows-1252 characters used by some English and Western European texts.

Graphic characters, format characters, control code characters, and private use characters are known collectively as assigned characters. Reserved code points are those code points which are available for use, but are not yet assigned. As of Unicode 15.0 there are 825,279 reserved code points.

Abstract characters

The set of graphic and format characters defined by Unicode does not correspond directly to the repertoire of abstract characters that is representable under Unicode. Unicode encodes characters by associating an abstract character with a particular code point. [64] 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. [65]

All graphic, format, and private use characters have a unique and immutable name by which they may be identified. This immutability has been guaranteed since Unicode version 2.0 by the Name Stability policy. [62] In cases where the name is seriously defective and misleading, or has a serious typographical error, a formal alias may be defined, and applications are encouraged to use the formal alias in place of the official character name. For example, U+A015YI SYLLABLE WU has the formal alias YI SYLLABLE ITERATION MARK, and U+FE18PRESENTATION FORM FOR VERTICAL RIGHT WHITE LENTICULAR BRAKCET ( sic ) has the formal alias PRESENTATION FORM FOR VERTICAL RIGHT WHITE LENTICULAR BRACKET. [66]

Ready-made versus composite characters

Unicode includes a mechanism for modifying characters that greatly extends the supported glyph repertoire. 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 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, é can be represented in Unicode as U+0065 (LATIN SMALL LETTER E) followed by U+0301 (COMBINING ACUTE ACCENT), but it can also be represented as the precomposed character U+00E9 (LATIN SMALL LETTER E WITH ACUTE). Thus, in many cases, users have multiple ways of encoding the same character. To deal with this, Unicode provides the mechanism of canonical equivalence.

An example of this arises with Hangul, the Korean alphabet. Unicode provides a mechanism for composing Hangul syllables with their individual subcomponents, known as Hangul Jamo. However, it also provides 11,172 combinations of precomposed syllables made from the most common jamo.

The CJK characters currently have codes only for their precomposed form. Still, most of those characters comprise simpler elements (called radicals), so in principle Unicode could have decomposed them as it did with Hangul. This would have greatly reduced the number of required code points, while allowing the display of virtually every conceivable character (which might do away with some of the problems caused by Han unification). A similar idea is used by some input methods, such as Cangjie and Wubi. However, attempts to do this for character encoding have stumbled over the fact that Chinese characters do not decompose as simply or as regularly as Hangul does.

A set of radicals was provided in Unicode 3.0 (CJK radicals between U+2E80 and U+2EFF, KangXi radicals in U+2F00 to U+2FDF, and ideographic description characters from U+2FF0 to U+2FFB), but the Unicode standard (ch. 12.2 of Unicode 5.2) warns against using ideographic description sequences as an alternate representation for previously encoded characters:

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 <U+0065, U+0301>.


JanaSanskritSans ddhrya.svg
The Devanāgarī ddhrya-ligature (द् + ध् + र् + य = द्ध्र्य) of JanaSanskritSans [67]
The Arabic lām-alif ligature (ل+ا=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: [68] MES-1 (Latin scripts only, 335 characters), MES-2 (Latin, Greek and Cyrillic 1062 characters) [69] and MES-3A & MES-3B (two larger subsets, not shown here). Note that MES-2 includes every character in MES-1 and WGL-4.

The standard DIN 91379 [70] 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 specification supports all official languages of European Union countries as well as the official languages of Iceland, Liechtenstein, Norway, and Switzerland, and also the German minority languages. 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
0020–7E Basic Latin (00–7F)
A0–FF Latin-1 Supplement (80–FF)
0100–13, 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 ...)
0218–1B, 1E–1FLatin 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)
0374–75, 7A, 7E, 84–8A, 8C, 8E–A1, A3–CE, D7, DA–E1 Greek (70–FF)
0400–5F, 90–91, 92–C4, C7–C8, CB–CC, D0–EB, EE–F5, F8–F9 Cyrillic (00–FF)
1E02–03, 0A–0B, 1E–1F, 40–41, 56–57, 60–61, 6A–6B, 80–85, 9B, F2–F3 Latin Extended Additional (00–FF)
1F00–15, 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)
2013–14, 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)
2105, 13, 16, 22, 26, 2E Letterlike Symbols (00–4F)
5B–5E Number Forms (50–8F)
90–93, 94–95, A8 Arrows (90–FF)
2200, 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)
2302, 0A, 20–21, 29–2A Miscellaneous Technical (00–FF)
2500, 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)
263A–3C, 40, 42, 60, 63, 65–66, 6A, 6B Miscellaneous Symbols (00–FF)
F0(01–02) Private Use Area (00–FF ...)
FB01–02 Alphabetic Presentation Forms (00–4F)
FFFD Specials

Rendering software which cannot process a Unicode character appropriately often displays it as an open rectangle, or the Unicode "replacement character" (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. [71] 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 uses one to four bytes per code point and, being compact for Latin scripts and ASCII-compatible, provides the de facto standard encoding for 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, code point U+FEFF, 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 (a character with no appearance and no effect other than preventing the formation of ligatures).

The same character converted to UTF-8 becomes the byte sequence EF BB BF. The Unicode Standard allows that the BOM "can serve as signature for UTF-8 encoded text where the character set is unmarked". [72] 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. Some programming languages, such as Seed7, use UTF-32 as internal representation for strings and characters. 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.


Unicode, in the form of UTF-8, has been the most common encoding for the World Wide Web since 2008. [73] 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 2023, UTF-8 accounts for on average 97.8% of all web pages (and 987 of the top 1,000 highest ranked web pages). [74] 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. [75] Over a third of the languages tracked have 100% UTF-8 use.

All internet protocols maintained by Internet Engineering Task Force, e.g. FTP, [76] 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". [77]

Operating systems

Unicode has become the dominant scheme for 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, 7, 8, 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) [78] 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

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, [79] 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 in a screen, such as with a character map program.

Online tools for finding the code point for a known character include Unicode Lookup [80] by Jonathan Hedley and Shapecatcher [81] 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.


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 [82] [83] a framework for internationalized email using UTF-8, and has updated [84] [85] [86] [87] 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.


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. [88]

Although syntax rules may affect the order in which characters are allowed to appear, XML (including XHTML) documents, by definition, [89] comprise characters from most of the Unicode code points, with the exception of:

HTML characters manifest either directly as bytes according to 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 &#916;, &#1049;, &#1511;, &#1605;, &#3671;, &#12354;, &#21494;, &#33865;, and &#47568; (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.


Unicode is not in principle concerned with fonts per se, seeing them as implementation choices. [90] 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. [91] 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.


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+2028LINE SEPARATOR and U+2029PARAGRAPH 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 Mac OS X 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.


Han unification

Han unification (the identification of forms in the East Asian languages which one can treat as stylistic variations of the same historical character) has become one of the most controversial aspects of Unicode, despite the presence of a majority of experts from all three regions in the Ideographic Research Group (IRG), which advises the Consortium and ISO on additions to the repertoire and on Han unification. [92]

Unicode has been criticized for failing to separately encode older and alternative forms of kanji which, critics argue, complicates the processing of ancient Japanese and uncommon Japanese names. This is often due to the fact that Unicode encodes characters rather than glyphs (the visual representations of the basic character that often vary from one language to another). Unification of glyphs leads to the perception that the languages themselves, not just the basic character representation, are being merged. [93] [ clarification needed ] There have been several attempts to create alternative encodings that preserve the stylistic differences between Chinese, Japanese, and Korean characters in opposition to Unicode's policy of Han unification. An example of one is TRON (although it is not widely adopted in Japan, there are some users who need to handle historical Japanese text and favor it).

Although the repertoire of fewer than 21,000 Han characters in the earliest version of Unicode was largely limited to characters in common modern usage, Unicode now includes more than 97,000 Han characters, and work is continuing to add thousands more historic and dialectal characters used in China, Japan, Korea, Taiwan, and Vietnam.

Modern font technology provides a means to address the practical issue of needing to depict a unified Han character in terms of a collection of alternative glyph representations, in the form of Unicode variation sequences. For example, the Advanced Typographic tables of OpenType permit one of a number of alternative glyph representations to be selected when performing the character to glyph mapping process. In this case, information can be provided within plain text to designate which alternate character form to select.

Various Cyrillic characters shown with upright, oblique and italic alternate forms Cyrillic cursive.svg
Various Cyrillic characters shown with upright, oblique and italic alternate forms

Italic or cursive characters in Cyrillic

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.

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 combining sequence of already existing characters can no longer be added to the standard in order 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+FF5EFULLWIDTH TILDE (in Microsoft Windows) or U+301CWAVE DASH (other vendors). [94]

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. [95] (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

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 (aka 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. [96] [97] [98] 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, [99] but these were rejected for encoding by the relevant ISO committee (ISO/IEC JTC 1/SC 2). [100]

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. [93] 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

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 e 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, 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, or AAT technologies for advanced rendering features.


The Unicode standard has imposed rules intended to guarantee stability. [101] 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 from then on, an assigned name to a code point would never change anymore. 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, [102] for example:

While Unicode defines the script designator (name) to be " Phags Pa ", in that script's character names a hyphen is added: U+A840PHAGS-PA LETTER KA. [105] [106]

Security issues

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, [107] and could also be used for manipulating the output of natural language processing (NLP) systems. [108]

Mitigation requires disallowing these characters, displaying them differently, or requiring that they resolve to the same identifier; all of this is complicated due to the huge and constantly changing set of characters. [109] [110]

A security advisory was released in 2021 from two researchers, one from the University of Cambridge and the other from the same and from the University of Edinburgh, in which they assert that the BIDI codes can be used to make large sections of code do something different from what they appear to do. [111]

See also


  1. The formal version reference is The Unicode Consortium: The Unicode Standard, Version 15.0.0. Mountain View, CA: The Unicode Consortium. 2022. ISBN   978-1-936213-32-0.
  2. Sometimes abbr.TUS is used. [1] [2]

Related Research Articles

<span class="mw-page-title-main">Character encoding</span> Using numbers to represent text characters

Character encoding is the process of assigning numbers to graphical characters, especially the written characters of human language, allowing them to be stored, transmitted, and transformed using digital computers. The numerical values that make up a character encoding are known as "code points" and collectively comprise a "code space", a "code page", or a "character map".

Web pages authored using HyperText Markup Language (HTML) may contain multilingual text represented with the Unicode universal character set. Key to the relationship between Unicode and HTML is the relationship between the "document character set", which defines the set of characters that may be present in a HTML document and assigns numbers to them, and the "external character encoding", or "charset", used to encode a given document as a sequence of bytes.

UTF-8 is a variable-length character encoding used for electronic communication. Defined by the Unicode Standard, the name is derived from UnicodeTransformation Format – 8-bit.

<span class="mw-page-title-main">UTF-16</span> Variable-width encoding of Unicode, using one or two 16-bit code units

UTF-16 (16-bit Unicode Transformation Format) is a character encoding capable of encoding all 1,112,064 valid code points of Unicode (in fact this number of code points is dictated by the design of UTF-16). The encoding is variable-length, as code points are encoded with one or two 16-bit code units. UTF-16 arose from an earlier obsolete fixed-width 16-bit encoding, now known as UCS-2 (for 2-byte Universal Character Set), once it became clear that more than 216 (65,536) code points were needed.

The byte order mark (BOM) is a particular usage of the special Unicode character, U+FEFFBYTE ORDER MARK, whose appearance as a magic number at the start of a text stream can signal several things to a program reading the text:

UTF-32 (32-bit Unicode Transformation Format) is a fixed-length encoding used to encode Unicode code points that uses exactly 32 bits (four bytes) per code point (but a number of leading bits must be zero as there are far fewer than 232 Unicode code points, needing actually only 21 bits). UTF-32 is a fixed-length encoding, in contrast to all other Unicode transformation formats, which are variable-length encodings. Each 32-bit value in UTF-32 represents one Unicode code point and is exactly equal to that code point's numerical value.

<span class="mw-page-title-main">Mojibake</span> Garbled text as a result of incorrect character encoding

Mojibake is the garbled text that is the result of text being decoded using an unintended character encoding. The result is a systematic replacement of symbols with completely unrelated ones, often from a different writing system.

UTF-7 is an obsolete variable-length character encoding for representing Unicode text using a stream of ASCII characters. It was originally intended to provide a means of encoding Unicode text for use in Internet E-mail messages that was more efficient than the combination of UTF-8 with quoted-printable.

The null character is a control character with the value zero. It is present in many character sets, including those defined by the Baudot and ITA2 codes, ISO/IEC 646, the C0 control code, the Universal Coded Character Set, and EBCDIC. It is available in nearly all mainstream programming languages. It is often abbreviated as NUL. In 8-bit codes, it is known as a null byte.

<span class="mw-page-title-main">GB 18030</span> Unicode character encoding mostly used for Simplified Chinese

GB 18030 is a Chinese government standard, described as Information Technology — Chinese coded character set and defines the required language and character support necessary for software in China. GB18030 is the registered Internet name for the official character set of the People's Republic of China (PRC) superseding GB2312. As a Unicode Transformation Format, GB18030 supports both simplified and traditional Chinese characters. It is also compatible with legacy encodings including GB2312, CP936, and GBK 1.0.

ISO/IEC 2022Information technology—Character code structure and extension techniques, is an ISO/IEC standard in the field of character encoding. Originating in 1971, it was most recently revised in 1994.

Extended Unix Code (EUC) is a multibyte character encoding system used primarily for Japanese, Korean, and simplified Chinese.

In character encoding terminology, a code point, codepoint or code position is a numerical value that maps to a specific character. Code points usually represent a single grapheme—usually a letter, digit, punctuation mark, or whitespace—but sometimes represent symbols, control characters, or formatting. The set of all possible code points within a given encoding/character set make up that encoding's codespace.

In Unicode, a Private Use Area (PUA) is a range of code points that, by definition, will not be assigned characters by the Unicode Consortium. Three private use areas are defined: one in the Basic Multilingual Plane, and one each in, and nearly covering, planes 15 and 16. The code points in these areas cannot be considered as standardized characters in Unicode itself. They are intentionally left undefined so that third parties may define their own characters without conflicting with Unicode Consortium assignments. Under the Unicode Stability Policy, the Private Use Areas will remain allocated for that purpose in all future Unicode versions.

This article compares Unicode encodings. Two situations are considered: 8-bit-clean environments, and environments that forbid use of byte values that have the high bit set. Originally such prohibitions were to allow for links that used only seven data bits, but they remain in some standards and so some standard-conforming software must generate messages that comply with the restrictions. Standard Compression Scheme for Unicode and Binary Ordered Compression for Unicode are excluded from the comparison tables because it is difficult to simply quantify their size.

UTF-1 is a method of transforming ISO/IEC 10646/Unicode into a stream of bytes. Its design does not provide self-synchronization, which makes searching for substrings and error recovery difficult. It reuses the ASCII printing characters for multi-byte encodings, making it unsuited for some uses. UTF-1 is also slow to encode or decode due to its use of division and multiplication by a number which is not a power of 2. Due to these issues, it did not gain acceptance and was quickly replaced by UTF-8.

A Unicode font is a computer font that maps glyphs to code points defined in the Unicode Standard. The vast majority of modern computer fonts use Unicode mappings, even those fonts which only include glyphs for a single writing system, or even only support the basic Latin alphabet. Fonts which support a wide range of Unicode scripts and Unicode symbols are sometimes referred to as "pan-Unicode fonts", although as the maximum number of glyphs that can be defined in a TrueType font is restricted to 65,535, it is not possible for a single font to provide individual glyphs for all defined Unicode characters. This article lists some widely used Unicode fonts that support a comparatively large number and broad range of Unicode characters.

<span class="mw-page-title-main">Universal Character Set characters</span> Complete list of the characters available on most computers

The Unicode Consortium and the ISO/IEC JTC 1/SC 2/WG 2 jointly collaborate on the list of the characters in the Universal Coded Character Set. The Universal Coded Character Set, most commonly called the Universal Character Set, is an international standard to map characters, discrete symbols used in natural language, mathematics, music, and other domains, to unique machine-readable data values. By creating this mapping, the UCS enables computer software vendors to interoperate, and transmit—interchange—UCS-encoded text strings from one to another. Because it is a universal map, it can be used to represent multiple languages at the same time. This avoids the confusion of using multiple legacy character encodings, which can result in the same sequence of codes having multiple interpretations depending on the character encoding in use, resulting in mojibake if the wrong one is chosen.

Specials is a short Unicode block of characters allocated at the very end of the Basic Multilingual Plane, at U+FFF0–FFFF. Of these 16 code points, five have been assigned since Unicode 3.0:

The Universal Coded Character Set is a standard set of characters defined by the international standard ISO/IEC 10646, Information technology — Universal Coded Character Set (UCS), which is the basis of many character encodings, improving as characters from previously unrepresented typing systems are added.


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Further reading