Unicode
Alias(es) |
|
---|---|
Language(s) | 168 scripts (list) |
Standard | Unicode Standard |
Encoding formats | (uncommon) (obsolete) |
Preceded by | ISO/IEC 8859, among others |
Unicode, formally The Unicode Standard,
Many common characters, including numerals, punctuation, and other symbols, are unified within the standard and are not treated as specific to any given writing system. Unicode encodes 3790 emoji, with the continued development thereof conducted by the Consortium as a part of the standard.[4] Moreover, the widespread adoption of Unicode was in large part responsible for the initial popularization of emoji outside of Japan. Unicode is ultimately capable of encoding more than 1.1 million characters.
Unicode has largely supplanted the previous environment of a myriad of incompatible
The Unicode
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. Of these, 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
The philosophy that underpins Unicode seeks to encode the underlying 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.
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.[6]
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).[7] 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.[8] With additional input from Peter Fenwick and Dave Opstad,[7] 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 scheme using 16-bit characters:[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.
This design decision was made based on the assumption that only scripts and characters in "modern" use would require encoding:[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 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 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 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. 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,[9] 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.[10]
Version 1.0 of Microsoft's TrueType specification, published in 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 (and few others) with any interest in text-processing standards, including Adobe, Apple, Google, IBM, Meta (previously as Facebook), Microsoft, Netflix, and SAP.[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
Unicode currently covers most major
As of 2024[update], a total of 168 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 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 Areas 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.
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]
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 2] 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.[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, 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.
Unicode 16.0, the latest version, was released on 10 September 2024. It added 5,185 characters and seven new scripts:
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.[20]
Version | Date | Publication (book, text) |
UCS edition | Total | Details | |
---|---|---|---|---|---|---|
Scripts | Characters[a] | |||||
1.0.0[21] | October 1991 | ISBN 0-201-56788-1 (vol. 1)
|
— | 24 | 7129 | Initial scripts covered: |
1.0.1[22] | June 1992 | ISBN 0-201-60845-6 (vol. 2) | 25 | 28327+21204 −6 |
The initial 20,902 CJK Unified Ideographs | |
1.1[23] | June 1993 | — | ISO/IEC 10646-1:1993 | 24 | 34168+5963 −9 |
33 reclassified as control characters. 4,306 Hangul syllables, Tibetan removed |
2.0[24] | July 1996 | ISBN 0-201-48345-9 | 25 | 38885+11373 −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 Areas allocated | |
2.1[25] | May 1998 | — | 38887+2 |
U+20AC € EURO SIGN, U+FFFC  OBJECT REPLACEMENT CHARACTER[25] | ||
3.0[26] | September 1999 | ISBN 0-201-61633-5 | ISO/IEC 10646-1:2000 | 38 | 49194+10307 |
patterns |
3.1[27] | March 2001 | — | ISO/IEC 10646-1:2000[c] ISO/IEC 10646-2:2001 |
41 | 94140+44946 |
Old Italic, sets of symbols for Western and Byzantine music , 42,711 additional CJK Unified Ideographs
|
3.2[28] | March 2002 | 45 | 95156+1016 |
Philippine scripts (Buhid, Hanunoo, Tagalog, and Tagbanwa) | ||
4.0[29] | April 2003 | ISBN 0-321-18578-1 | ISO/IEC 10646:2003 | 52 | 96382+1226 |
Tai Le, and Ugaritic, Hexagram symbols
|
4.1[30] | March 2005 | — | 59 | 97655+1273 |
Greek numbers and musical symbols, first named character sequences were introduced.[31]
| |
5.0[32] | July 2006 | ISBN 0-321-48091-0 | 64 | 99024+1369 |
Balinese, cuneiform, N'Ko, ʼPhags-pa, Phoenician[33] | |
5.1[34] | April 2008 | — | 75 | 100648+1624 |
U+1E9E ẞ LATIN CAPITAL LETTER SHARP S
| |
5.2[35] | October 2009 | ISBN 978-1-936213-00-9 | 90 | 107296+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[36] | October 2010 | ISBN 978-1-936213-01-6 | ISO/IEC 10646:2010 | 93 | 109384+2088 |
emoticons and emoji,[37] additional CJK Unified Ideographs
|
6.1[38] | January 2012 | ISBN 978-1-936213-02-3 | ISO/IEC 10646:2012 | 100 | 110116+732 |
Chakma, Meroitic cursive, Meroitic hieroglyphs, Miao, Sharada, Sora Sompeng, and Takri |
6.2[39] | September 2012 | ISBN 978-1-936213-07-8 | 110117+1 |
U+20BA ₺ TURKISH LIRA SIGN | ||
6.3[40] | September 2013 | ISBN 978-1-936213-08-5 | 110122+5 |
5 bidirectional formatting characters | ||
7.0[41] | June 2014 | ISBN 978-1-936213-09-2 | 123 | 112956+2834 |
Mro, Nabataean, Old North Arabian, Old Permic, Pahawh Hmong, Palmyrene, Pau Cin Hau, Psalter Pahlavi, Siddham, Tirhuta, Warang Citi, and dingbats
| |
8.0[42] | June 2015 | ISBN 978-1-936213-10-8 | ISO/IEC 10646:2014 | 129 | 120672+7716 |
Old Hungarian, SignWriting, additional CJK Unified Ideographs, lowercase letters for Cherokee, 5 emoji skin tone modifiers
|
9.0[45] | June 2016 | ISBN 978-1-936213-13-9 | 135 | 128172+7500 |
Adlam, Bhaiksuki, Marchen, Newa, Osage, Tangut, 72 emoji[46] | |
10.0[47] | June 2017 | ISBN 978-1-936213-16-0 | ISO/IEC 10646:2017 | 139 | 136690+8518 |
|
11.0[48] | June 2018 | ISBN 978-1-936213-19-1 | 146 | 137374+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[49] | March 2019 | ISBN 978-1-936213-22-1 | 150 | 137928+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[50] | May 2019 | ISBN 978-1-936213-25-2 | 137929+1 |
U+32FF ㋿ SQUARE ERA NAME REIWA | ||
13.0[51] | March 2020 | ISBN 978-1-936213-26-9 | ISO/IEC 10646:2020 | 154 | 143859+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[53] | September 2021 | ISBN 978-1-936213-29-0 | 159 | 144697+838 |
musical notation, 37 emoji | |
15.0[54] | September 2022 | ISBN 978-1-936213-32-0 | 161 | 149186+4489 |
Kawi and Mundari, 20 emoji, 4,192 CJK ideographs, control characters for Egyptian hieroglyphs | |
15.1[55] | September 2023 | ISBN 978-1-936213-33-7 | 149813+627 |
Additional CJK ideographs | ||
16.0[56] | September 2024 | ISBN 978-1-936213-34-4 | 168 | 154998+5185 |
Tulu-Tigalari
|
- 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;[43]
9.0 added Amendment 2, as well as Adlam, Newa, Japanese TV symbols, and 74 emoji and symbols.[44] - ^
- 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.
Projected versions
The Unicode Consortium normally releases a new version of The Unicode Standard once a year. Version 17.0, the next major version, is projected to include 4301 new unified CJK characters.[57][58]
Architecture and terminology
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 1114111, 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,[62] and the code points themselves are written as hexadecimal numbers. 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 𓉔 EGYPTIAN HIEROGLYPH O004 () is not padded.[63]
There are a total of 220 + (216 − 211) = 1112064 valid code points within the codespace. (This number arises from the limitations of the UTF-16 character encoding, which can encode the 216 code points in the range U+0000 through U+FFFF except for the 211 code points in the range U+D800 through U+DFFF, which are used as surrogate pairs to encode the 220 code points in the range U+10000 through U+10FFFF.)
Code planes and blocks
The Unicode codespace is divided into 17 planes, numbered 0 to 16. Plane 0 is the
Within each plane, characters are allocated within named
General Category property
Each code point is assigned a classification, listed as the code point's
General Category (Unicode Character Property)[a] | |||||
---|---|---|---|---|---|
Value | Category Major, minor | Basic type[b] | Character assigned[b] | Count[c] (as of 16.0) |
Remarks |
L, Letter; LC, Cased Letter (Lu, Ll, and Lt only)[d] | |||||
Lu | Letter, uppercase | Graphic | Character | 1,858 | |
Ll | Letter, lowercase | Graphic | Character | 2,258 | |
Lt | Letter, titlecase | Graphic | Character | 31 | Dz )
|
Lm | Letter, modifier | Graphic | Character | 404 | A modifier letter |
Lo | Letter, other | Graphic | Character | 136,477 | An unicase alphabet
|
M, Mark | |||||
Mn | Mark, nonspacing | Graphic | Character | 2,020 | |
Mc | Mark, spacing combining | Graphic | Character | 468 | |
Me | Mark, enclosing | Graphic | Character | 13 | |
N, Number | |||||
Nd | Number, decimal digit | Graphic | Character | 760 | All these, and only these, have Numeric Type = De[e] |
Nl | Number, letter | Graphic | Character | 236 | Numerals composed of letters or letterlike symbols (e.g., Roman numerals) |
No | Number, other | Graphic | Character | 915 | E.g., subscript digits, vigesimal digits
|
P, 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.[f] |
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 | 640 | |
S, Symbol | |||||
Sm | Symbol, math | Graphic | Character | 950 | , which despite frequent use as mathematical operators, are primarily considered to be "punctuation". |
Sc | Symbol, currency | Graphic | Character | 63 | Currency symbols |
Sk | Symbol, modifier | Graphic | Character | 125 | |
So | Symbol, other | Graphic | Character | 7,376 | |
Z, Separator | |||||
Zs | Separator, space | Graphic | Character | 17 | Includes the space, but not TAB, CR, or LF, which are Cc |
Zl | Separator, line | Format | Character | 1 | Only U+2028 LINE SEPARATOR (LSEP) |
Zp | Separator, paragraph | Format | Character | 1 | Only U+2029 PARAGRAPH SEPARATOR (PSEP) |
C, Other | |||||
Cc | Other, control | Control | Character | 65 (will never change)[e] | No name,[g] <control> |
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)[e] | No name,[g] <surrogate> |
Co | Other, private use | Private-use | Character (but no interpretation specified) | 137,468 total (will never change) BMP, 131,068 in Planes 15–16 ) |
No name,[g] <private-use> |
Cn | Other, not assigned | Noncharacter | Not | 66 (will not change unless the range of Unicode code points is expanded)[e] | No name,[g] <noncharacter> |
Reserved | Not | 819,467 | No name,[g] <reserved> | ||
|
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.[64] 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 1111998 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[65] 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 (65534 characters),
- Supplementary Private Use Area-B: U+100000–U+10FFFD (65534 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 16.0, there are 154826 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
65 code points, the ranges U+0000–U+001F and U+007F–U+009F, are reserved as control codes, corresponding to the
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 15.1, there are 819467 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 representable under Unicode. Unicode encodes characters by associating an abstract character with a particular code point.
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.[64] 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 ꀕ 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 BRACKET.[68]
Ready-made versus composite characters
Unicode includes a mechanism for modifying characters that greatly extends the supported repertoire of glyphs. This covers the use of
An example of this arises with the Korean alphabet
The
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>.
Ligatures
Many scripts, including
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
The standard DIN 91379[72] 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.
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
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.[73] 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 either one or two 16-bit units per code point, but cannot encode surrogate characters
- 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
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".
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 an 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.
Adoption
Unicode, in the form of UTF-8, has been the most common encoding for the World Wide Web since 2008.[75] 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).[76] 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.[77] Over a third of the languages tracked have 100% UTF-8 use.
All internet protocols maintained by
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, 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)[80] 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
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,[81] 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[82] by Jonathan Hedley and Shapecatcher[83] 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[84][85] a framework for internationalized email using UTF-8, and has updated[86][87][88][89] several protocols in accordance with that framework.
The adoption of Unicode in email has been very slow.[
Web
All
Although syntax rules may affect the order in which characters are allowed to appear, XML (including XHTML) documents, by definition,[91] 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
Fonts
Unicode is not in principle concerned with fonts per se, seeing them as implementation choices.[92] 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.[93] 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
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
Issues
Character unification
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.[94]
Existing character set standards such as the Japanese
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
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 16.0, the standard now encodes more than 97,000 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'
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. The same OpenType 'locl' technique is used.[99]
Localised case pairs
For use in the
By contrast, the
Diacritics on lowercase I
Whether the lowercase letter I is expected to retain its tittle when a diacritic applies also depends on local conventions.
Security
Unicode has a large number of
A security advisory was released in 2021 by two researchers, one from the
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.
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.
Indic scripts
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
technologies for advanced rendering features.Anomalies
The Unicode Standard has imposed rules intended to guarantee stability.[116] 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,[117] for example:
- U+034F ͏ COMBINING GRAPHEME JOINER: Does not join graphemes.[117]
- U+2118 ℘ SCRIPT CAPITAL P: This is a small letter. The capital is U+1D4AB 𝒫 MATHEMATICAL SCRIPT CAPITAL P.[118]
- U+A015 ꀕ 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.[119] (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 ꡀ PHAGS-PA LETTER KA.[120][121] This, however, is not an anomaly, but the rule: hyphens are replaced by underscores in script designators.[120]
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
- ^ Sometimes abbreviated as TUS.[1][2]
- ^ "A Unicode Standard Annex (UAX) forms an integral part of The Unicode Standard, but is published as a separate document."[1]
- ^ a code point is an abstract representation of an UCS character by an integer between 0 and 1,114,111 (1,114,112 = 220 + 216 or 17 × 216 = 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).
References
- ISBN 978-1-936213-34-4.
- ^ "Unicode Technical Report #28: Unicode 3.2". Unicode Consortium. 2002-03-27. Retrieved 2022-06-23.
- ^ Jenkins, John H. (2021-08-26). "Unicode Standard Annex #45: U-source Ideographs". Unicode Consortium. §2.2 The Source Field. Retrieved 2022-06-23.
- ^
- "Unicode Character Count V16.0". The Unicode Consortium. 2024-09-10.
- "Unicode 16.0 Versioned Charts Index". The Unicode Consortium. 2024-09-10.
- "Supported Scripts". The Unicode Consortium. 2024-09-10. Retrieved 2024-09-11.
- ^ "Emoji Counts, v16.0". The Unicode Consortium. Retrieved 2024-09-10.
- ^ "The Unicode Standard: A Technical Introduction". 2019-08-22. Retrieved 2024-09-11.
- ^ "Unicode Bulldog Award". Unicode. Archived from the original on 2023-11-11.
- ^ Xerox PARC. Many persons contributed ideas to the development of a new encoding design. Beginning in 1980, these efforts evolved into the Xerox Character Code Standard (XCCS) by the present author, a multilingual encoding that has been maintained by Xerox as an internal corporate standard since 1982, through the efforts of Ed Smura, Ron Pellar, and others.(ideographic character unification). Unicode retains the many features of XCCS whose utility has been proved over the years in an international line of communication multilingual system products.
Unicode arose as the result of eight years of working experience with XCCS. Its fundamental differences from XCCS were proposed by Peter Fenwick and Dave Opstad (pure 16-bit codes) and by Lee Collins - ^ "Summary Narrative". Unicode. 2006-08-31. Retrieved 2010-03-15.
- ^ "History of Unicode Release and Publication Dates". Unicode. Retrieved 2023-03-20.
- ^ Searle, Stephen J. "Unicode Revisited". Retrieved 2013-01-18.
- ^ a b "The Unicode Consortium Members". Retrieved 2024-02-12.
- ^ "Unicode FAQ". Retrieved 2020-04-02.
- ^ "Supported Scripts". Unicode. Retrieved 2022-09-16.
- ^ "Roadmap to the BMP". Unicode Consortium. Retrieved 2018-07-30.
- ^ "Roadmaps to Unicode". Unicode. Archived from the original on 2023-12-08.
- ^ "script encoding initiative". Berkeley Linguistics. Archived from the original on 2023-03-25.
- ^ "About The Script Encoding Initiative". The Unicode Consortium. Retrieved 2012-06-04.
- ^ "Unicode 6.1 Paperback Available". announcements_at_unicode.org. Retrieved 2012-05-30.
- ^ "Unicode 16.0.0". Unicode. Retrieved 2024-09-13.
- ^ "Enumerated Versions of The Unicode Standard". Retrieved 2016-06-21.
- ^
- The Unicode Standard, Version 1.0.0. Mountain View, CA: The Unicode Consortium. October 1991.
- "1.0.0/UnicodeData.txt (reconstructed)". 2004. Retrieved 2010-03-16.
- ^
- The Unicode Standard, Version 1.0.1. Mountain View, CA: The Unicode Consortium. June 1992.
- "Unicode Data 1.0.1". Retrieved 2010-03-16.
- ^
- The Unicode Standard, Version 1.1.5. Mountain View, CA: The Unicode Consortium. July 1995.
- "Unicode Data 1995". Retrieved 2010-03-16.
- ^
- The Unicode Standard, Version 2.0.0. Mountain View, CA: The Unicode Consortium. July 1996.
- "Unicode Data-2.0.14". Retrieved 2010-03-16.
- ^ a b
- The Unicode Standard, Version 2.1.2. Mountain View, CA: The Unicode Consortium. May 1998.
- "Unicode Data-2.1.2". Retrieved 2010-03-16.
- ^
- The Unicode Standard, Version 3.0.0. Mountain View, CA: The Unicode Consortium. September 1999.
- "Unicode Data-3.0.0". Retrieved 2023-10-02.
- ^
- The Unicode Standard, Version 3.1.0. Mountain View, CA: The Unicode Consortium. March 2001.
- "Unicode Data-3.1.0". Retrieved 2023-10-02.
- ^
- The Unicode Standard, Version 3.2.0. Mountain View, CA: The Unicode Consortium. March 2002.
- "Unicode Data-3.2.0". Retrieved 2023-10-02.
- . Retrieved 2023-10-02.