Unicode, formally The Unicode Standard,
[The formal version reference is ] is an
information technology standard Standard may refer to:
Symbols
* Colours, standards and guidons, kinds of military signs
* Standard (emblem), a type of a large symbol or emblem used for identification
Norms, conventions or requirements
* Standard (metrology), an object ...
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
The Unicode Consortium (legally Unicode, Inc.) is a 501(c)(3) non-profit organization incorporated and based in Mountain View, California. Its primary purpose is to maintain and publish the Unicode Standard which was developed with the intentio ...
, defines as of the current version (15.0) 149,186 characters covering 161 modern and historic
scripts
Script may refer to:
Writing systems
* Script, a distinctive writing system, based on a repertoire of specific elements or symbols, or that repertoire
* Script (styles of handwriting)
** Script typeface, a typeface with characteristics of handw ...
, 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
Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing arbitrary data. It defines a set of rules for encoding documents in a format that is both human-readable and machine-readable. T ...
, 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
Collation is the assembly of written information into a standard order. Many systems of collation are based on numerical order or alphabetical order, or extensions and combinations thereof. Collation is a fundamental element of most office fil ...
, rendering, and
bidirectional text
A bidirectional text contains two text directionalities, right-to-left (RTL) and left-to-right (LTR). It generally involves text containing different types of alphabets, but may also refer to boustrophedon, which is changing text direction in ea ...
display order for multilingual texts, and so on. 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
ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because of ...
-compatible
UTF-8, the ASCII-incompatible
UTF-16
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 cod ...
(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 character
The Latin script, also known as Roman script, is an alphabetic writing system based on the letters of the classical Latin alphabet, derived from a form of the Greek alphabet which was in use in the ancient Greek city of Cumae, in southern Ita ...
s 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—
grapheme
In linguistics, a grapheme is the smallest functional unit of a writing system.
The word ''grapheme'' is derived and the suffix ''-eme'' by analogy with ''phoneme'' and other names of emic units. The study of graphemes is called ''graphemics' ...
s and grapheme-like units—rather than the variant
glyph
A glyph () is any kind of purposeful mark. In typography, a glyph is "the specific shape, design, or representation of a character". It is a particular graphical representation, in a particular typeface, of an element of written language. A g ...
s (renderings) for such characters. In the case of
Chinese characters
Chinese characters () are logograms developed for the writing of Chinese. In addition, they have been adapted to write other East Asian languages, and remain a key component of the Japanese writing system where they are known as ''kanji ...
, this sometimes leads to controversies over distinguishing the underlying character from its variant glyphs (see
Han unification
Han unification is an effort by the authors of Unicode and the Universal Character Set to map multiple character sets of the Han characters of the so-called CJK languages into a single set of unified characters. Han characters are a feature ...
).
In text processing, Unicode takes the role of providing a unique —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
In metal typesetting, a font is a particular size, weight and style of a typeface. Each font is a matched set of type, with a piece (a "sort") for each glyph. A typeface consists of a range of such fonts that shared an overall design.
In mod ...
, 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
Ken Roger Lunde (, born 12 August 1965 in Madison, Wisconsin)Lunde, 2008. is an American specialist in information processing for East Asian languages.
Academic Background
Ken majored in linguistics at University of Wisconsin–Madison in 1985, ...
, and
Michael Everson
Michael Everson (born January 9, 1963) is an American and Irish linguist, script encoder, typesetter, type designer and publisher. He runs a publishing company called Evertype, through which he has published over a hundred books since 2006.
...
.
History
Based on experiences with the
Xerox Character Code Standard (XCCS) since 1980,
the origins of Unicode can be traced back to 1987, when
Joe Becker from
Xerox with
Lee Collins and
Mark Davis Mark Davis may refer to:
Entertainers
*Mark Davis (talk show host), American radio talk show host
*Mark Jonathan Davis (born 1965), American actor/singer and creator of Richard Cheese
*Mark Davis, American bassist and founding member for the band ...
from
Apple started investigating the practicalities of creating a universal character set. With additional input from Peter Fenwick and
Dave Opstad,
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".
In this document, entitled ''Unicode 88'', Becker outlined a
16-bit
16-bit microcomputers are microcomputers that use 16-bit microprocessors.
A 16-bit register can store 216 different values. The range of integer values that can be stored in 16 bits depends on the integer representation used. With the two mos ...
character model:
Unicode is intended to address the need for a workable, reliable world text encoding. Unicode could be roughly described as "wide-body ASCII
ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because of ...
" 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:
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
The Unicode Consortium (legally Unicode, Inc.) is a 501(c)(3) non-profit organization incorporated and based in Mountain View, California. Its primary purpose is to maintain and publish the Unicode Standard which was developed with the intentio ...
was incorporated in California on 3 January 1991, 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.
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
Adobe ( ; ) is a building material made from earth and organic materials. is Spanish for ''mudbrick''. In some English-speaking regions of Spanish heritage, such as the Southwestern United States, the term is used to refer to any kind of e ...
,
Apple,
Facebook,
Google,
IBM,
Microsoft,
Netflix, and
SAP SE.
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)
The Ministry of Awqaf and Religious Affairs (MARA) is the governmental body in the Sultanate of Oman responsible for overseeing all matters related to awqaf and religious affairs.
The current Minister of Awqaf and Religious Affairs is Abdullah ...
is a full member with voting rights.
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
writing systems in use today.
, a total of 161
scripts
Script may refer to:
Writing systems
* Script, a distinctive writing system, based on a repertoire of specific elements or symbols, or that repertoire
* Script (styles of handwriting)
** Script typeface, a typeface with characteristics of handw ...
are included in the latest version of Unicode (covering
alphabet
An alphabet is a standardized set of basic written graphemes (called letter (alphabet), letters) that represent the phonemes of certain spoken languages. Not all writing systems represent language in this way; in a syllabary, each character ...
s,
abugida
An abugida (, from Ge'ez: ), sometimes known as alphasyllabary, neosyllabary or pseudo-alphabet, is a segmental writing system in which consonant-vowel sequences are written as units; each unit is based on a consonant letter, and vowel not ...
s 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
Michael Everson (born January 9, 1963) is an American and Irish linguist, script encoder, typesetter, type designer and publisher. He runs a publishing company called Evertype, through which he has published over a hundred books since 2006.
...
, Rick McGowan, Ken Whistler, V.S. Umamaheswaran) maintain the list of scripts that are candidates or potential candidates for encoding and their tentative code block assignments on the Unicode Roadmap page of the
Unicode Consortium
The Unicode Consortium (legally Unicode, Inc.) is a 501(c)(3) non-profit organization incorporated and based in Mountain View, California. Its primary purpose is to maintain and publish the Unicode Standard which was developed with the intentio ...
website. For some scripts on the Roadmap, such as
Jurchen Jurchen may refer to:
* Jurchen people, Tungusic people who inhabited the region of Manchuria until the 17th century
** Haixi Jurchens, a grouping of the Jurchens as identified by the Chinese of the Ming Dynasty
** Jianzhou Jurchens, a grouping of ...
and
Khitan small script
The Khitan small script () was one of two writing systems used for the now-extinct Khitan language (the other was the Khitan large script). It was used during the 10th–12th century by the Khitan people, who had created the Liao Empire in present ...
, 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
The Tengwar script is an artificial script, one of several scripts created by J. R. R. Tolkien, the author of ''The Lord of the Rings''.
Within the fictional context of Middle-earth, the Tengwar were invented by the Elf Fëanor, and used f ...
) 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, 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.
Versions
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
Collation is the assembly of written information into a standard order. Many systems of collation are based on numerical order or alphabetical order, or extensions and combinations thereof. Collation is a fundamental element of most office fil ...
and rendering. It also provides a comprehensive catalog of character properties, including those needed for supporting
bidirectional text
A bidirectional text contains two text directionalities, right-to-left (RTL) and left-to-right (LTR). It generally involves text containing different types of alphabets, but may also refer to boustrophedon, which is changing text direction in ea ...
, 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.
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.
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.
Architecture and terminology
Codespace and Code Points
The Unicode Standard defines a ''codespace,''
a set of numerical values ranging from 0 through 10FFFF
16, called ''
code points''
and denoted as through ("U+" followed by the code point value in
hexadecimal, which is prepended with
leading zeros to a minimum of four digits; ''e. g.'', for the division sign but (''not'' ) for the
Egyptian hieroglyph .). Of these 2
16 + 2
20 defined code points, the code points from through , which are used to encode surrogate pairs in
UTF-16
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 cod ...
, are reserved by the Unicode Standard and may not be used to encode valid characters, resulting in a net total of 2
16 − 2
11 + 2
20 = 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
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 cod ...
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
A general officer is an officer of high rank in the armies, and in some nations' air forces, space forces, and marines or naval infantry.
In some usages the term "general officer" refers to a rank above colonel."general, adj. and n.". OED On ...
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:
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
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 cod ...
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.
[
] Like surrogates, the rule that these cannot be used is often ignored, although the operation of the
byte order mark
The byte order mark (BOM) is a particular usage of the special Unicode character, , whose appearance as a magic number at the start of a text stream can signal several things to a program reading the text:
* The byte order, or endianness, of th ...
(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 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:
* Private Use Area: U+E000–U+F8FF (6,400 characters),
* Supplementary Private Use Area-A: U+F0000–U+FFFFD (65,534 characters),
* Supplementary Private Use Area-B: U+100000–U+10FFFD (65,534 characters).
Graphic characters are characters defined by Unicode to have particular semantics, and either have a visible
glyph
A glyph () is any kind of purposeful mark. In typography, a glyph is "the specific shape, design, or representation of a character". It is a particular graphical representation, in a particular typeface, of an element of written language. A g ...
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, and 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
The C0 and C1 control code or control character sets define control codes for use in text by computer systems that use ASCII and derivatives of ASCII. The codes represent additional information about the text, such as the position of a cursor ...
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. 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
The acute accent (), , is a diacritic used in many modern written languages with alphabets based on the Latin, Cyrillic, and Greek scripts. For the most commonly encountered uses of the accent in the Latin and Greek alphabets, precomposed cha ...
, which is required in
Lithuanian
Lithuanian may refer to:
* Lithuanians
* Lithuanian language
* The country of Lithuania
* Grand Duchy of Lithuania
* Culture of Lithuania
* Lithuanian cuisine
* Lithuanian Jews as often called "Lithuanians" (''Lita'im'' or ''Litvaks'') by other Jew ...
, 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.
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.
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, has the formal alias , and has the formal alias .
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 mark
In digital typography, combining characters are characters that are intended to modify other characters. The most common combining characters in the Latin script are the combining diacritical marks (including combining accents).
Unicode also ...
s 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 () followed by U+0301 (), but it can also be represented as the precomposed character U+00E9 (). 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
In internationalization, CJK characters is a collective term for the Chinese, Japanese, and Korean languages, all of which include Chinese characters and derivatives in their writing systems, sometimes paired with other scripts. Collectively, ...
currently have codes only for their precomposed form. Still, most of those characters comprise simpler elements (called
radicals
Radical may refer to:
Politics and ideology Politics
*Radical politics, the political intent of fundamental societal change
*Radicalism (historical), the Radical Movement that began in late 18th century Britain and spread to continental Europe and ...
), 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
Han unification is an effort by the authors of Unicode and the Universal Character Set to map multiple character sets of the Han characters of the so-called CJK languages into a single set of unified characters. Han characters are a feature ...
). A similar idea is used by some
input method
An input method (or input method editor, commonly abbreviated IME) is an operating system component or program that enables users to generate characters not natively available on their input devices by using sequences of characters (or mouse o ...
s, such as
Cangjie
Cangjie () is a legendary ancient Chinese figure said to have been an official historian of the Yellow Emperor and the inventor of Chinese characters.
Legend has it that he had four eyes, and that when he invented the characters, the deities a ...
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
Radical may refer to:
Politics and ideology Politics
*Radical politics, the political intent of fundamental societal change
*Radicalism (historical), the Radical Movement that began in late 18th century Britain and spread to continental Europe and ...
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
The Chinese character description languages are several proposed languages to most accurately and completely describe Chinese (or CJK) characters and information such as their list of components, list of strokes (basic and complex), their order, a ...
as an alternate representation for previously encoded characters:
Ligatures
Many scripts, including
Arabic
Arabic (, ' ; , ' or ) is a Semitic language spoken primarily across the Arab world.Semitic languages: an international handbook / edited by Stefan Weninger; in collaboration with Geoffrey Khan, Michael P. Streck, Janet C. E.Watson; Walte ...
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
OpenType is a format for scalable computer fonts. It was built on its predecessor TrueType, retaining TrueType's basic structure and adding many intricate data structures for prescribing typographic behavior. OpenType is a registered trademark ...
(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: MES-1 (Latin scripts only, 335 characters), MES-2 (Latin, Greek and Cyrillic 1062 characters) 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
The DIN standard DIN 91379: "Characters and defined character sequences in Unicode for the electronic processing of names and data exchange in Europe, with CD-ROM" defines a normative subset of Unicode Latin characters, sequences of base characte ...
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.
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. 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-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 mult ...
). 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 for each code point, maximizes compatibility with
ASCII
ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because of ...
*
UTF-EBCDIC, similar to UTF-8 but designed for compatibility with
EBCDIC
Extended Binary Coded Decimal Interchange Code (EBCDIC; ) is an eight- bit character encoding used mainly on IBM mainframe and IBM midrange computer operating systems. It descended from the code used with punched cards and the corresponding ...
(not part of ''The Unicode Standard'')
*
UTF-16
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 cod ...
, uses one or two 16-bit code units per code point, cannot encode surrogates
*
UTF-32
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 co ...
, uses one 32-bit code unit per code point
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
The byte order mark (BOM) is a particular usage of the special Unicode character, , whose appearance as a magic number at the start of a text stream can signal several things to a program reading the text:
* The byte order, or endianness, of th ...
(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
Ligature may refer to:
* Ligature (medicine), a piece of suture used to shut off a blood vessel or other anatomical structure
** Ligature (orthodontic), used in dentistry
* Ligature (music), an element of musical notation used especially in the me ...
).
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". Some software developers have adopted it for other encodings, including UTF-8, in an attempt to distinguish UTF-8 from local 8-bit
code page
In computing, a code page is a character encoding and as such it is a specific association of a set of printable characters and control characters with unique numbers. Typically each number represents the binary value in a single byte. (In some ...
s. However , 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
In computer architecture, 32-bit computing refers to computer systems with a processor, memory, and other major system components that operate on data in 32-bit units. Compared to smaller bit widths, 32-bit computers can perform large calculati ...
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
Python may refer to:
Snakes
* Pythonidae, a family of nonvenomous snakes found in Africa, Asia, and Australia
** ''Python'' (genus), a genus of Pythonidae found in Africa and Asia
* Python (mythology), a mythical serpent
Computing
* Python (pr ...
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
High-level and low-level, as technical terms, are used to classify, describe and point to specific goals of a systematic operation; and are applied in a wide range of contexts, such as, for instance, in domains as widely varied as computer scien ...
coded software.
Punycode, another encoding form, enables the encoding of Unicode strings into the limited character set supported by the
ASCII
ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because of ...
-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
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 ...
of the
People's Republic of China (PRC).
BOCU-1 and
SCSU are Unicode compression schemes. The
April Fools' Day RFC of 2005 specified two
parody UTF encodings,
UTF-9 and
UTF-18.
Adoption
Unicode, in the form of
UTF-8, has been the most common encoding for the
World Wide Web
The World Wide Web (WWW), commonly known as the Web, is an information system enabling documents and other web resources to be accessed over the Internet.
Documents and downloadable media are made available to the network through web se ...
since 2008.
It has near-universal adoption, and much of the non-UTF-8 content is found in other Unicode encodings, e.g.
UTF-16
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 cod ...
. , UTF-8 accounts for on average 97.8% of all web pages (and 988 of the top 1,000 highest ranked web pages).
Although many pages only use
ASCII
ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because of ...
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. Over a third of the languages tracked have 100% UTF-8 use.
All internet protocols maintained by
Internet Engineering Task Force, e.g.
FTP, have required support for UTF-8 since the publication of in 1998, which specified that all IETF protocols "MUST be able to use the UTF-8 charset".
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
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 cod ...
(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
File:2000 Events Collage.png, From left, clockwise: Protests against Bush v. Gore after the 2000 United States presidential election; Heads of state meet for the Millennium Summit; The International Space Station in its infant form as seen from S ...
,
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
KDE is an international free software community that develops free and open-source software. As a central development hub, it provides tools and resources that allow collaborative work on this kind of software. Well-known products include the ...
also use it for internal representation. Partial support for Unicode can be installed on
Windows 9x
Windows 9x is a generic term referring to a series of Microsoft Windows computer operating systems produced from 1995 to 2000, which were based on the Windows 95 kernel and its underlying foundation of MS-DOS, both of which were updated in subs ...
through the
Microsoft Layer for Unicode.
UTF-8 (originally developed for
Plan 9) 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
The World Wide Web (WWW), commonly known as the Web, is an information system enabling documents and other web resources to be accessed over the Internet.
Documents and downloadable media are made available to the network through web se ...
.
Multilingual text-rendering engines which use Unicode include
Uniscribe and
DirectWrite for Microsoft Windows,
ATSUI and
Core Text for macOS, and
Pango
Pango (stylized as Παν語) is a text (i.e. glyph) layout engine library which works with the HarfBuzz shaping engine for displaying multi-language text.
Full-function rendering of text and cross-platform support is achieved when Pango is use ...
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 ISO/IEC 14755 is a joint ISO and IEC standard for input methods to enter characters defined in ISO/IEC 10646, the international standard corresponding to the Unicode Standard. As the repertoires of ISO/IEC 10646 and the Unicode Standard are identic ...
, 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 by Jonathan Hedley and Shapecatcher by Benjamin Milde. In Unicode Lookup, one enters a search key (e.g. "fractions"), and a list of corresponding characters with their code points is returned. In Shapecatcher, based on
Shape context, one draws the character in a box and a list of characters approximating the drawing, with their code points, is returned.
Email
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
In computer programming, Base64 is a group of binary-to-text encoding schemes that represent binary data (more specifically, a sequence of 8-bit bytes) in sequences of 24 bits that can be represented by four 6-bit Base64 digits.
Common to all bi ...
or the
Quoted-printable transfer encoding are recommended, depending on whether much of the message consists of
ASCII
ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because of ...
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 a framework for internationalized email using UTF-8, and has updated several protocols in accordance with that framework.
The adoption of Unicode in email has been very slow. Some East Asian text is still encoded in encodings such as
ISO-2022
ISO/IEC 2022 ''Information technology—Character code structure and extension techniques'', is an ISO/IEC standard (equivalent to the ECMA standard ECMA-35, the ANSI standard ANSI X3.41 and the Japanese Industrial Standard JIS X 0202) in the f ...
, and some devices, such as mobile phones, still cannot correctly handle Unicode data. Support has been improving, however. Many major free mail providers such as
Yahoo! Mail,
Gmail, and
Outlook.com
Outlook.com is a webmail service that is part of the Microsoft 365 product family. It offers mail, calendaring, contacts, and tasks services.
Founded in 1996 by Sabeer Bhatia and Jack Smith as Hotmail, it was acquired by Microsoft in 1997 ...
support it.
Web
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
In metal typesetting, a font is a particular size, weight and style of a typeface. Each font is a matched set of type, with a piece (a "sort") for each glyph. A typeface consists of a range of such fonts that shared an overall design.
In mod ...
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.
Although syntax rules may affect the order in which characters are allowed to appear,
XML
Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing arbitrary data. It defines a set of rules for encoding documents in a format that is both human-readable and machine-readable. T ...
(including
XHTML) documents, by definition, comprise characters from most of the Unicode code points, with the exception of:
* most of the
C0 control codes,
* the permanently unassigned code points D800–DFFF,
* FFFE or FFFF.
HTML characters manifest either directly as
byte
The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable uni ...
s 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
Δ
,
Й
,
ק
,
م
,
๗
,
あ
,
叶
,
葉
, and
말
(or the same numeric values expressed in hexadecimal, with
&#x
as the prefix) should display on all browsers as Δ, Й, ק ,م, ๗, あ, 叶, 葉, and 말.
When specifying
URIs, for example as
URLs in
HTTP
The Hypertext Transfer Protocol (HTTP) is an application layer protocol in the Internet protocol suite model for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web, w ...
requests, non-ASCII characters must be
percent-encoded.
Fonts
Unicode is not in principle concerned with fonts ''per se'', seeing them as implementation choices. Any given character may have many
allograph
Allography, from the Greek for "other writing", has several meanings which all relate to how words and sounds are written down.
Authorship
An allograph may be the opposite of an autograph – i.e. a person's words or name (signature) written by so ...
s, 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. 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
font
In metal typesetting, a font is a particular size, weight and style of a typeface. Each font is a matched set of type, with a piece (a "sort") for each glyph. A typeface consists of a range of such fonts that shared an overall design.
In mod ...
s based on Unicode are widely available, since
TrueType
TrueType is an outline font standard developed by Apple in the late 1980s as a competitor to Adobe's Type 1 fonts used in PostScript. It has become the most common format for fonts on the classic Mac OS, macOS, and Microsoft Windows operating ...
and
OpenType
OpenType is a format for scalable computer fonts. It was built on its predecessor TrueType, retaining TrueType's basic structure and adding many intricate data structures for prescribing typographic behavior. OpenType is a registered trademark ...
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
In metal typesetting, a font is a particular size, weight and style of a typeface. Each font is a matched set of type, with a piece (a "sort") for each glyph. A typeface consists of a range of such fonts that shared an overall design.
In mode ...
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
In economics, diminishing returns are the decrease in marginal (incremental) output of a production process as the amount of a single factor of production is incrementally increased, holding all other factors of production equal (ceteris pari ...
for most typefaces.
Newlines
Unicode partially addresses the
newline problem that occurs when trying to read a text file on different platforms. Unicode defines a large number of
characters
Character or Characters may refer to:
Arts, entertainment, and media Literature
* ''Character'' (novel), a 1936 Dutch novel by Ferdinand Bordewijk
* ''Characters'' (Theophrastus), a classical Greek set of character sketches attributed to The ...
that conforming applications should recognize as line terminators.
In terms of the newline, Unicode introduced and . 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.
Issues
Han unification
Han unification
Han unification is an effort by the authors of Unicode and the Universal Character Set to map multiple character sets of the Han characters of the so-called CJK languages into a single set of unified characters. Han characters are a feature ...
(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 The Ideographic Research Group (IRG), formerly called the Ideographic Rapporteur Group, is a subgroup of Working Group 2 (WG2) of ISO/IEC JTC 1/SC 2 (SC 2), the subcommittee of the Joint Technical Committee of ISO and IEC which is responsible for ...
(IRG), which advises the Consortium and ISO on additions to the repertoire and on Han unification.
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.
[The secret life of Unicode: A peek at Unicode's soft underbelly](_blank)
Suzanne Topping, 1 May 2001 ''(Internet Archive)'' 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
''Tron'' (stylized as ''TRON'') is a 1982 American science fiction action-adventure film written and directed by Steven Lisberger from a story by Lisberger and Bonnie MacBird. The film stars Jeff Bridges as Kevin Flynn, a computer programmer an ...
(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
OpenType is a format for scalable computer fonts. It was built on its predecessor TrueType, retaining TrueType's basic structure and adding many intricate data structures for prescribing typographic behavior. OpenType is a registered trademark ...
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.
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
In digital typography, combining characters are characters that are intended to modify other characters. The most common combining characters in the Latin script are the combining diacritical marks (including combining accents).
Unicode also ...
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
Extended Unix Code (EUC) is a multibyte character encoding system used primarily for Japanese, Korean, and simplified Chinese.
The most commonly used EUC codes are variable-length encodings with a character belonging to an compliant coded char ...
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 (in
Microsoft Windows) or (other vendors).
Some Japanese computer programmers objected to Unicode because it requires them to separate the use of and , which was mapped to 0x5C in JIS X 0201, and a lot of legacy code exists with this usage. (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. 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, but these were rejected for encoding by the relevant ISO committee (
ISO/IEC JTC 1/SC 2).
Thai alphabet
The Thai script ( th, อักษรไทย, ) is the abugida used to write Thai, Southern Thai and many other languages spoken in Thailand. The Thai alphabet itself (as used to write Thai) has 44 consonant symbols ( th, พยัญชน� ...
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.
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 "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
The acute accent (), , is a diacritic used in many modern written languages with alphabets based on the Latin, Cyrillic, and Greek scripts. For the most commonly encountered uses of the accent in the Latin and Greek alphabets, precomposed cha ...
, 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.. 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
Charis SIL is a transitional serif typeface developed by SIL International based on Bitstream Charter, one of the first fonts designed for laser printers. The font offers four family members: roman, bold, italic, and bold italic.
Its design goal ...
that uses
Graphite,
OpenType
OpenType is a format for scalable computer fonts. It was built on its predecessor TrueType, retaining TrueType's basic structure and adding many intricate data structures for prescribing typographic behavior. OpenType is a registered trademark ...
, or
AAT technologies for advanced rendering features.
Anomalies
The Unicode standard has imposed rules intended to guarantee stability. 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 for 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,
for example:
* : This is a small letter. The capital is .
* : Does not join graphemes.
* : This is not a Yi syllable, but a Yi iteration mark.
* : ''bracket'' is spelled incorrectly. (Spelling errors are resolved by using
Unicode alias names.)
While Unicode defines the script designator (name) to be "", in that script's character names a hyphen is added: .
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, and could also be used for manipulating the output of
natural language processing (NLP) systems.
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.
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.
See also
*
Comparison of Unicode encodings
*
Religious and political symbols in Unicode
*
International Components for Unicode (ICU), now as ICU-
TC a part of Unicode
*
List of binary codes This is a list of some binary codes that are (or have been) used to represent text as a sequence of binary digits "0" and "1". Fixed-width binary codes use a set number of bits to represent each character in the text, while in variable-width binary ...
*
List of Unicode characters
*
List of XML and HTML character entity references
In SGML, HTML and XML documents, the logical constructs known as ''character data'' and ''attribute values'' consist of sequences of characters, in which each character can manifest directly (representing itself), or can be represented by a series ...
*
Open-source Unicode typefaces
*
Standards related to Unicode
*
Unicode symbols
*
Universal Coded Character Set
*
Lotus Multi-Byte Character Set (LMBCS), a parallel development with similar intentions
Notes
References
Further reading
* ''The Unicode Standard, Version 3.0'', The Unicode Consortium, Addison-Wesley Longman, Inc., April 2000.
* ''The Unicode Standard, Version 4.0'', The Unicode Consortium, Addison-Wesley Professional, 27 August 2003.
* ''The Unicode Standard, Version 5.0, Fifth Edition'', The
Unicode Consortium
The Unicode Consortium (legally Unicode, Inc.) is a 501(c)(3) non-profit organization incorporated and based in Mountain View, California. Its primary purpose is to maintain and publish the Unicode Standard which was developed with the intentio ...
, Addison-Wesley Professional, 27 October 2006.
* Julie D. Allen. ''The Unicode Standard, Version 6.0'', The
Unicode Consortium
The Unicode Consortium (legally Unicode, Inc.) is a 501(c)(3) non-profit organization incorporated and based in Mountain View, California. Its primary purpose is to maintain and publish the Unicode Standard which was developed with the intentio ...
, Mountain View, 2011, ,
.
* ''The Complete Manual of Typography'', James Felici, Adobe Press; 1st edition, 2002.
* ''Unicode: A Primer'', Tony Graham, M&T books, 2000. .
* ''Unicode Demystified: A Practical Programmer's Guide to the Encoding Standard'', Richard Gillam, Addison-Wesley Professional; 1st edition, 2002.
* ''Unicode Explained'', Jukka K. Korpela, O'Reilly; 1st edition, 2006.
*
External links
*
Latest Unicode Standard* Th
Unicode Character Database text documentlisting the names, code points and properties of all Unicode characters
*
Alan Wood's Unicode Resourcescontains lists of word processors with Unicode capability; fonts and characters are grouped by type; characters are presented in lists, not grids.
The World’s Writing Systems all 294 known writing systems with their Unicode status (131 not yet encoded)
Unicode BMP Fallback Fontdisplays the Unicode 6.1 value of any character in a document, including in the Private Use Area, rather than the glyph itself.
{{Authority control
Unicode,
Character encoding
Digital typography