The Unicode Standard, Version 5.0
In
computer science, 'Unicode' is an
industry standard allowing
computers to consistently represent and manipulate
text expressed in any of the world's
writing systems. Developed in tandem with the
Universal Character Set standard and published in book form as ''The Unicode Standard'', Unicode consists of a repertoire of about 100,000
characters, a set of code charts for visual reference, an encoding methodology and set of standard
character encodings, an enumeration of character properties such as upper and lower
case, a set of reference data
computer files, and a number of related items, such as character properties, rules for
text normalization, decomposition,
collation, rendering and bidirectional display order (for the correct display of text containing both right-to-left scripts, such as
Arabic or
Hebrew, and left-to-right scripts).
[1]
The
Unicode Consortium, the non-profit organization that coordinates Unicode's development, 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.
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
XML, the
Java programming language and modern
operating systems.
Origin and development
Unicode has the explicit aim of transcending the limitations of traditional
character encodings, such as those defined by the
ISO 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
Roman characters and the local language) but not multilingual computer processing (computer processing of arbitrary languages mixed with each other).
Unicode, in intent, encodes the underlying
characters —
graphemes and grapheme-like units — rather than the variant
glyphs (renderings) for such characters. In the case of
Chinese characters, this sometimes leads to controversies over distinguishing the underlying character from its variant glyphs (see
Han unification).
In text processing, Unicode takes the role of providing a unique ''code point'' — a number, not a glyph — for each character. In other words, Unicode represents a character in an abstract way and leaves the visual rendering (size, shape,
font or style) to other software, such as a
web browser or
word processor. This simple aim becomes complicated, however, by 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 8859-1 so as to make it trivial to convert existing western text. A lot of 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 Latin alphabet that is separate from the main Latin alphabet section. In Chinese, Japanese and Korean (
CJK) fonts, these characters are rendered at the same width as CJK
ideographs rather than at half the width. For other examples, see
Duplicate characters in Unicode.
When writing about a Unicode character, it is normal to write "U+" followed by a hexadecimal number indicating the character's code point. For code points in the BMP, four digits are used; for code points outside the BMP, five or six digits are used, as required. Older versions of the standard used similar notations, but with slightly different rules. For example, Unicode 3.0 used "U-" followed by eight digits, and allowed "U+" to be used only with exactly four digits in order to indicate a code unit, not a code point.
Standard
The
Unicode Consortium, based in
California, develops the Unicode standard. Any company or individual willing to pay the membership dues may join this organization. Members include virtually all of the main computer software and hardware companies with any interest in text-processing standards, such as
Adobe Systems,
Apple,
HP,
IBM,
Microsoft,
Xerox and many others.
The Consortium first published ''The Unicode Standard'' (ISBN 0-321-18578-1) in 1991, and continues to develop standards based on that original work. Unicode is developed in conjunction with the
International Organization for Standardization and shares the character repertoire with
ISO/IEC 10646: the Universal Character Set. Unicode and ISO/IEC 10646 function equivalently as character encodings, but ''The Unicode Standard'' contains much more information for implementers, covering — in depth — topics such as bitwise encoding,
collation and rendering. The Unicode Standard enumerates a multitude of character properties, including those needed for supporting
bidirectional text. The two standards do use slightly different terminology.
In 2005, the 100,000th character to be entered into the pipeline for standardisation was the MALAYALAM PRASLESHAM. It was encoded based on the contribution by
Rachana Akshara Vedi.
Unicode revisions thus far:
★ Unicode 1.0: October 1991
[2]
★ Unicode 1.0.1: June 1992
[3]
★ Unicode 1.1: June 1993
[4]
★ Unicode 2.0: July 1996
[5]
★ Unicode 2.1: May 1998
★ Unicode 2.1.2: May 1998
[6]
★ Unicode 3.0: September 1999. Covered 16-bit UCS
Basic Multilingual Plane from ISO 10646-1:2000.
[7]
★ Unicode 3.1: March 2001. Added
Supplementary Planes from ISO 10646-2, providing supplementary characters
★ Unicode 3.2: March 2002
★ Unicode 4.0: April 2003
[8]
★ Unicode 4.0.1: March 2004
★ Unicode 4.1: March 2005
★ Unicode 5.0: July 2006
[9]
★ Unicode 5.1: expected early or mid 2008
Scripts covered
Unicode covers almost all scripts (
writing systems) in current use today.
[10]
Although more than 30
writing systems (
alphabets,
syllabaries, and others) are included in Unicode, there remain many more still awaiting encoding. 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.
Michael Everson, Rick McGowan, and Ken Whistler maintain the list of such scripts and their tentative code block assignments on the
Unicode Consortium Web site, at
Unicode Roadmap. For some scripts on the Roadmap, encoding proposals have been made and are working their way through the approval process. For others, no proposal can be made until the scholarly communities involved can agree on the character repertoire and other details.
Among the scripts awaiting encoding are
Egyptian Hieroglyphics, Babylonian and other
cuneiforms,
Phoenician, and
Mayan, together with lesser-known scripts of Asia, Europe, Africa, and the Americas. Many of them are not understood, such as the
Rongorongo of
Easter Island,
Linear A of
Crete, and
Meroitic of the Upper
Nile.
Invented scripts, most of which do not qualify for inclusion in Unicode due to lack of real-world usage, are listed in the
ConScript Unicode Registry, along with unofficial but widely-used
Private Use Area code assignments. Similarly, many medieval letter variants and ligatures not in Unicode are encoded in the
Medieval Unicode Font Initiative. In 1997
Michael Everson made a proposal to encode the characters of the artificial
Klingon language in Plane 1 of
ISO/IEC 10646-2.
[11] The Unicode Consortium rejected this proposal in 2001 as "inappropriate for encoding" — not because of any technical inadequacy, but because users of Klingon normally read, write and exchange data in
Latin transliteration. Proposals suggested the inclusion of the
elvish scripts
Tengwar and
Cirth from
J. R. R. Tolkien's fictional
Middle-earth setting in Plane 1 in 1993.
[12] The Consortium withdrew the draft to incorporate changes suggested by
Tolkienists, and as of 2005 it remains under consideration. Both Klingon and the Tolkien scripts have assignments in the ConScript Unicode Registry.
Mapping and encodings
Several mechanisms have been specified for implementing Unicode; which one implementers choose depends on available storage space,
source code compatibility, and interoperability with other systems.
Unicode defines two mapping methods: the ''
Unicode Transformation Format'' (UTF) encodings, and the ''
Universal 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 values''. The numbers in the names of the encodings indicate the number of bits in one code value (for UTF encodings) or the number of bytes per code value (for UCS) encodings. UTF-8 and UTF-16 are probably 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-7 — a relatively unpopular 7-bit encoding, often considered obsolete (not part of ''The Unicode Standard'' but rather an RFC)
★
UTF-8 — an 8-bit, variable-width encoding, which maximizes compatibility with
ASCII.
★
UTF-EBCDIC — an 8-bit variable-width encoding, which maximizes compatibility with
EBCDIC. (not part of ''The Unicode Standard'')
★
UTF-16 — a 16-bit, variable-width encoding
★
UTF-32 — a 32-bit, fixed-width encoding
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 also used by most recent
Linux distributions as a direct replacement for legacy encodings in general text handling.
The UCS-2 and UTF-16 encodings specify the Unicode
Byte Order Mark (BOM) for use at the beginnings of text files, which may be used for byte ordering detection (or
byte endianness detection). Some software developers have adopted it for other encodings, including UTF-8, which does not need an indication of byte order. In this case it attempts to mark the file as containing Unicode text. 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 other places, other than the beginning of text, conveys the zero-width no-break space (a character with no appearance and no effect other than preventing the formation of
ligatures). Also, the units
FE and
FF never appear in
UTF-8. The same character converted to UTF-8 becomes the byte sequence
EF BB BF.
In UTF-32 and UCS-4, one 32-bit code value serves as a fairly direct representation of any character's code point (although the endianness, which varies across different platforms, affects how the code value actually manifests as an octet sequence). In the other cases, each code point may be represented by a variable number of code values. UTF-32 is widely used as internal representation of text in programs (as opposed to stored or transmitted text), since every Unix operating system which uses the
gcc compilers to generate software uses it as the standard "wide character" encoding. Recent versions of the
python programming language (beginning with 2.2) may also be configured to use UTF-32 as the representation for unicode strings, effectively disseminating such encoding in
high-level coded software.
Punycode, another encoding form, enables the encoding of Unicode strings into the limited character set supported by the
ASCII-based
Domain Name System. The encoding is used as part of
IDNA, which is a system enabling the use of
Internationalized Domain Names in all languages that are supported by Unicode.
GB18030 is another encoding form for Unicode, from the
Standardization Administration of China. It is the official
character set of the
People's Republic of China (PRC).
The
April Fools' Day RFC of 2005 specified two
parody UTF encodings,
UTF-9 and UTF-18.
Ready-made versus composite characters
Unicode includes a mechanism for modifying character shape and so greatly extending the supported glyph repertoire. This covers the use of
combining diacritical marks. They get inserted after the main character (one can stack several combining diacritics over 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 (Latin small letter e) followed by U+0301 (combining acute) but it can also be represented as the precomposed character U+00E9 (Latin small letter e with acute). So in many cases, users have many 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 the mechanism for composing Hangul syllables with their individual subcomponents, known as
Hangul Jamo. However, it also provides all 11,172 combinations of precomposed Hangul syllables.
The
CJK ideographs currently have codes only for their precomposed form. Still, most of those ideographs evidently comprise simpler elements (radicals), so in principle Unicode could have decomposed them just as it has happened with
Hangul. This would have greatly reduced the number of required code points, while allowing the display of virtually every conceivable ideograph (which might do away with some of the problems caused by the
Han unification). A similar idea covers some
input methods, such as
Cangjie and
Wubi. However, attempts to do this for character encoding have stumbled over the fact that ideographs do not actually decompose as simply or as regularly as it seems they should.
A set of
radicals was provided in Unicode 3.0 (CJK radicals between U+2E80 and U+2EFF, KangXi radicals in U+2F00 to U+2FDF, and ideographic description characters from U+2FF0 to U+2FFB), but the Unicode standard (ch. 11.1 of Unicode 4.1) warns against using ideographic description sequences as an alternate representation for previously encoded characters:
Ligatures
Many scripts, including
Arabic and
Devanagari, have special orthographic rules which require that certain combinations of letterforms be combined into special
ligature forms. The rules governing ligature formation can be quite complex, requiring special script-shaping technologies such as
OpenType (by Adobe and Microsoft),
Graphite (by
SIL International), or
AAT (by Apple).
Instructions are also embedded in fonts to tell the
operating system how to properly output different character sequences. A simple solution to the placement of combining marks or diacritics is assigning the marks a width of zero and placing the glyph itself to the left or right of the left
sidebearing (depending on the direction of the script they are intended to be used with). A mark handled this way will appear over whatever character precedes it, but will not adjust its position relative to the width or height of the base glyph; it may be visually awkward and it may overlap some glyphs. Real stacking is impossible, but can be approximated in limited cases (for example, Thai top-combining vowels and tone marks can just be at different heights to start with). Generally this approach is only effective in monospaced fonts but can also be used as a fallback rendering method when more complex methods fail.
As of 2004, most software still cannot reliably handle many features not supported by older font formats, so combining characters generally will not work correctly. For example, (precomposed e with macron and acute above) and (e followed by the combining macron above and combining acute above) should be rendered identically, both appearing as an
e with a
macron and
acute accent, but in practice, their appearance can vary greatly across software applications. Similarly,
underdots, as needed in the
romanization of
Indic, will often be placed incorrectly. As a workaround, Unicode characters that map to precomposed glyphs can be used for many such characters. The need for such alternatives inherits from the limitations of fonts and rendering technology, not weaknesses of Unicode itself.
Standardized subsets
Several subsets of Unicode are standardized: Microsoft Windows since Windows NT 4.0 supports
WGL-4 with 652 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:
[13]
MES-1 (Latin scripts only, 335 characters), MES-2 (Latin, Greek and Cyrillic 1062 characters)
[14] and MES-3A & MES-3B (two larger subsets, not shown here). Note that MES-2 includes every character in MES-1, which in turn includes all of WGL-4.
| 'WGL-4', ''MES-1'' and MES-2 |
| Row | Cells | Range(s) |
|---|---|---|
| 00 | '''20–7E''' | Basic Latin (00–7F) |
|---|---|---|
| '''A0–FF''' | Latin-1 Supplement (80–FF) |
| 01 | '''00–13,'' 14–15, ''16–2B,'' 2C–2D, ''2E–4D,'' 4E–4F, ''50–7E,'' 7F' | Latin Extended-A (00–7F) |
|---|
| 8F, '92,' B7, DE-EF, 'FA–FF' | Latin Extended-B (80–FF …) |
| 02 | 18–1B, 1E–1F | Latin Extended-B (… 00–4F) |
|---|
| 59, 7C, 92 | IPA Extensions (50–AF) |
| BB–BD, 'C6, ''C7,'' C9,' D6, '''D8–DB,'' DC, ''DD,''' DF, EE | Spacing Modifier Letters (B0–FF) |
| 03 | 74–75, 7A, 7E, '84–8A, 8C, 8E–A1, A3–CE,' D7, DA–E1 | Greek (70–FF) |
|---|
| 04 | 00, '01–0C,' 0D, '0E–4F,' 50, '51–5C,' 5D, '5E–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' | General Punctuation (00–6F) |
|---|
| '44,' 4A, '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 which cannot process a Unicode character appropriately most often display it as only 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. The Apple ''
LastResort'' font will display a substitute glyph indicating the Unicode range of the character and the
SIL Unicode fallback font will display a box showing the hexadecimal scalar value of the character.
Unicode in use
Operating systems
Unicode has become the dominant scheme for internal processing and sometimes storage (though a lot of text is still stored in legacy encodings) of text. Early adopters tended to use UCS-2 and later moved to UTF-16 (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,
Windows 2000 and
Windows XP), which uses Unicode as the sole internal character encoding. The
Java and
.NET bytecode environments, Mac OS X, and
KDE also use it for internal representation.
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.
Multilingual text-rendering engines which use Unicode include
Uniscribe for Microsoft Windows,
ATSUI for Mac OS X and
Pango, a
free software engine used by
GTK+ (and hence 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 14755[15] describes methods for entering Unicode characters from their codepoints; clause 5.1 describes a ''Basic method'' whereby a ''beginning sequence'' is followed by the hexadecimal representation of the codepoint and ther ''ending sequence''; an example of an ISO 14755-conformant system is
GNOME, where the beginning sequence is CTRL+SHIFT+U and the ending sequence is null. In various operating systems,
alt codes can be used to input Unicode points; where the code point of the desired character is known, it is possible to create Unicode characters by pressing
Alt + PLUS + #, where # represents the hexadecimal code point; for example,
Alt + PLUS + F + 1 will produce the Unicode character ''ñ''. On some systems, this is limited to the BMP (characters up to U+FFFF).
ISO 14755 also describes a ''screen-selection entry method''; in
Microsoft Windows (since Windows 2000), the "Character Map" program (Start/Programs/Accessories/System Tools/Character Map) provides browsing and rich-text editing controls for all Table I characters in the BMP, by selection from a drop-down table, assuming that a Unicode
font is selected. Mac OS X (version 10.2 and newer),
KDE and
GNOME have similar utilities.
E-mail
Main articles: Unicode and e-mail
MIME defines two different mechanisms for encoding non-ASCII characters in
e-mail, depending on whether the characters are in e-mail 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 e-mail transmission of Unicode the UTF-8 character set and the
Base64 transfer encoding are recommended. The details of the two different mechanisms are specified in the MIME standards and are generally hidden from users of e-mail software.
The adoption of Unicode in
e-mail has been very slow. Some East-Asian text is still encoded in a local encoding such as
Shift-JIS, and some devices, such as cell phones, still cannot handle Unicode data correctly. Support has been improving however.
Web
Main articles: Unicode and HTML
All
W3C recommendations have used Unicode as their ''document character set'' since HTML 4.0.
Web browsers have supported Unicode, especially UTF-8, for many years. Display problems result primarily from
font related issues. In particular
Internet Explorer does not render many code points unless it is explicitly told to use a font that contains them.
Although syntax rules may affect the order in which characters are allowed to appear, both
HTML 4 and
XML (including
XHTML) documents, by definition, comprise characters from most of the Unicode code points, with the exception of:
★ most of the
C0 and C1 control codes
★ the permanently-unassigned code points D800–DFFF
★ any code point ending in FFFE or FFFF
These characters manifest either directly as
bytes according to document's encoding, if the encoding supports them, or users may write them as numeric character references with
percent-encoding based on the character's Unicode code point. For example, the references
Δ,
Й,
ק,
م,
๗,
あ,
叶,
葉, and
냻 (or the same numeric values expressed in hexadecimal, with
&#x as the prefix) display on browsers as Δ, Й, ק, م, ๗, あ, 叶, 葉, and 냻. In
HTTP requests,
URLs must be percent-encoded.
Fonts
Free and retail
fonts based on Unicode are commonly available, since
TrueType and
OpenType support Unicode. These font formats map Unicode code points to glyphs.
Thousands of
fonts exist on the market, but fewer than a dozen fonts — sometimes described as "pan-Unicode" fonts — attempt to support the majority of Unicode's character repertoire. Instead, Unicode-based
fonts typically focus on supporting only basic ASCII and particular scripts or sets of characters or symbols. Several reasons justify this approach: applications and documents rarely need to render characters from more than one or two writing systems; fonts tend to demand resources in computing environments; and operating systems and applications show increasing intelligence in regard to obtaining glyph information from separate font files as needed, i.e.
font substitution. Furthermore, designing a consistent set of rendering instructions for tens of thousands of glyphs constitutes a monumental task; such a venture passes the point of
diminishing returns for most typefaces.
Issues
Philosophical and completeness criticisms
Han unification (the identification of forms in the three
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 Rapporteur Group (IRG), which advises the Consortium and ISO on additions to the repertoire and on Han unification.
[16]
Unicode has been criticized for failing to allow for older and alternative forms of
kanji which, critics argue, complicates the processing of ancient Japanese and uncommon Japanese names, although it follows the recommendations of Japanese language scholars and of the Japanese government and contains all of the same characters as previous widely used encoding standards.
[ The secret life of Unicode: A peek at Unicode's soft underbelly, Suzanne Topping, 1 May 2001] There have been several attempts to create an alternative encodings that preserve the minor, stylistic differences between Chinese, Japanese, and Korean characters in opposition to Unicode's policy of
Han unification. Among them are
TRON (although it is not widely adopted in Japan, there are some users who need to handle historical Japanese text and favor it), and
UTF-2000.
Many older forms were not included in early versions of the Unicode standard, but Unicode 4.0 contains more than 70,000 Han characters and work continues on adding characters from the early literature of China, Korea, and Japan. Some argue, however, that this is not satisfactory, pointing out as an example the need to create new characters, representing words in various
Chinese dialects, more of which may be invented in the future.
Despite these problems, the official encoding of China,
GB-18030, supports the full range of characters in Unicode.
Mapping to legacy character sets
Injective mappings must be provided between characters in existing legacy character sets and characters in Unicode to facilitate conversion to Unicode and allow interoperability with legacy software. Lack of consistency in various mappings between earlier Japanese encodings such as
Shift-JIS or
EUC-JP and Unicode led to
round-trip format conversion mismatches, particularly the mapping of the character JIS X 201 '～' (1-33, WAVE DASH), heavily used in legacy database data, to either '～' U+FF5E FULLWIDTH TILDE (in
Microsoft Windows) or '〜' U+301C WAVE DASH (other vendors).
[17]
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 there is a lot of legacy code with this usage.
[18] (This encoding also replaces tilde '~' 0x7E with overline '¯', now 0xAF.) The separation of these characters exists in ISO 8859-1, from long before Unicode.
Indic scripts
Thai language support has been criticized for its illogical 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
logical 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. This ordering problem complicates the Unicode collation process slightly, requiring table lookups to reorder Thai characters for collation.
Indic scripts of India itself such as Hindi, Tamil and Telugu 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 out of components. Some local scholars argued in favor of assignments of Unicode codepoints to these ligatures, going against the practice for other writing systems, though Unicode contains some Arabic and other ligatures for back compatibility purposes only. [19] [20] [21] 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 Tibetan script (the Chinese National Standard organization failed to achieve a similar change).
See also
★ Comparison of Unicode encodings
★ Free software Unicode typefaces
★ List of Unicode characters
★ List of XML and HTML character entity references
Notes
1. http://www.unicode.org/standard/principles.html#What_Characters
2. ISBN 0-201-56788-1
3. ISBN 0-201-60845-6
4. Previous 2 Publications, and, Unicode Technical Report #4:The Unicode Standard, Version 1.1 by Mark Davis
5. ISBN 0-201-48345-9
6. Previous 3 Publications, and, Unicode Technical Report #8, The Unicode Standard, Version 2.1 by Lisa Moore
7. ISBN 0-201-61633-5
8. ISBN 0-321-18578-1
9. (The character database, aka. ''UCD'', published on 18 July 2006; the book, ''The Unicode Standard, Version 5.0'' was released on 9 November 2006. ISBN 0321480910
10. http://www.unicode.org/charts/
11. http://std.dkuug.dk/JTC1/SC2/WG2/docs/n1643/n1643.htm
12. http://std.dkuug.dk/JTC1/SC2/WG2/docs/n1641/n1641.htm http://std.dkuug.dk/JTC1/SC2/WG2/docs/n1642/n1642.htm
13. CWA 13873:2000 - Multilingual European Subsets in ISO/IEC 10646-1 CEN Workshop Agreement 13873
14. Multilingual European Character Set 2 (MES-2) Rationale, Markus Kuhn, 1998
15. ISO/IEC JTC1/SC 18/WG 9 N
16. A Brief History of Character Codes, Steven J. Searle, originally written 1999, last updated 2004
17.
AFII contribution about WAVE DASH,
Unicode vendor-specific character table for Japanese
18. ''ISO 646-
★ Problem'', Section 4.4.3.5 of ''Introduction to I18n'', Tomohiro KUBOTA, 2001
19. http://www.unicode.org/charts/PDF/UFB50.pdf
20. http://www.unicode.org/charts/PDF/UFE70.pdf
21. http://www.unicode.org/charts/PDF/UFB00.pdf
References
★ ''The Unicode Standard, Version 5.0, Fifth Edition'', The Unicode Consortium, Addison-Wesley Professional, 27 October 2006. ISBN 0-321-48091-0
★ ''The Unicode Standard, Version 4.0'', The Unicode Consortium, Addison-Wesley Professional, 27 August 2003. ISBN 0-321-18578-1
★ ''The Complete Manual of Typography'', James Felici, Adobe Press; 1st edition, 2002. ISBN 0-321-12730-7
★ ''Unicode: A Primer'', Tony Graham, M&T books, 2000. ISBN 0-7645-4625-2.
★ ''Unicode Demystified: A Practical Programmer's Guide to the Encoding Standard'', Richard Gillam, Addison-Wesley Professional; 1st edition, 2002. ISBN 0-201-70052-2
★ ''Unicode Explained'', Jukka K. Korpela, O'Reilly; 1st edition, 2006. ISBN 0-596-10121-X
External links
★ The Unicode Consortium
★ decodeunicode.org images of all 98,884 graphical unicode characters (german/english, full text search)
★ UniView
★ Unicode Character Search (search for characters by their unicode names)
★ Table of Unicode characters from 1 to 65535
★ UTF-8, UTF-16, UTF-32 Code Charts and a character map (requires JavaScript)
★ Tim Bray's Characters vs Bytes explains how the different encodings work.
★ Alan Wood's Unicode Resources Contains lists of word processors with Unicode capability; fonts and characters are grouped by type; characters are presented in lists, not grids.
★ libUniCode-plus Wiki (creation and manipulation of Unicode tables)
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