Specials (Unicode block)

Last updated
Specials
RangeU+FFF0..U+FFFF
(16 code points)
Plane BMP
Scripts Common
Assigned5 code points
Unused9 reserved code points
2 non-characters
Unicode version history
1.0.01 (+1)
2.12 (+1)
3.05 (+3)
Note: [1] [2]

Specials is a short Unicode block allocated at the very end of the Basic Multilingual Plane, at U+FFF0FFFF. Of these 16 code points, five are assigned as of Unicode 12.0:

Unicode Character encoding standard

Unicode is a computing industry standard for the consistent encoding, representation, and handling of text expressed in most of the world's writing systems. The standard is maintained by the Unicode Consortium, and as of May 2019 the most recent version, Unicode 12.1, contains a repertoire of 137,994 characters covering 150 modern and historic scripts, as well as multiple symbol sets and emoji. The character repertoire of the Unicode Standard is synchronized with ISO/IEC 10646, and both are code-for-code identical.

Contents

In linguistics and pedagogy, an interlinear gloss is a gloss placed between lines, such as between a line of original text and its translation into another language. When glossed, each line of the original text acquires one or more lines of transcription known as an interlinear text or interlinear glossed text (IGT)—interlinear for short. Such glosses help the reader follow the relationship between the source text and its translation, and the structure of the original language. In its simplest form, an interlinear gloss is simply a literal, word-for-word translation of the source text.

In computing, a compound document is a document type typically produced using word processing software, and is a regular text document intermingled with non-text elements such as spreadsheets, pictures, digital videos, digital audio, and other multimedia features. It can also be used to collect several documents into one.

FFFE and FFFF are not unassigned in the usual sense, but guaranteed not to be Unicode characters at all. They can be used to guess a text's encoding scheme, since any text containing these is by definition not a correctly encoded Unicode text. Unicode's U+FEFF BYTE ORDER MARK character can be inserted at the beginning of a Unicode text to signal its endianness: a program reading such a text and encountering 0xFFFE would then know that it should switch the byte order for all the following characters.

In computing, endianness refers to the order of bytes within a binary representation of a number. It can also be used more generally to refer to the internal ordering of any representation, such as the digits in a numeral system or the sections of a date.

Replacement character

Replacement character Replacement character.svg
Replacement character

The replacement character � (often a black diamond with a white question mark or an empty square box) is a symbol found in the Unicode standard at code point U+FFFD in the Specials table. It is used to indicate problems when a system is unable to render a stream of data to a correct symbol. It is usually seen when the data is invalid and does not match any character:

Consider a text file containing the German word "für" in the ISO-8859-1 encoding (0x66 0xFC 0x72). This file is now opened with a text editor that assumes the input is UTF-8. The first and last byte are valid UTF-8 encodings of ASCII, but the middle byte (0xFC) is not a valid byte in UTF-8. Therefore, a text editor could replace this byte with the replacement character symbol to produce a valid string of Unicode code points. The whole string now displays like this: "f�r".

A text file is a kind of computer file that is structured as a sequence of lines of electronic text. A text file exists stored as data within a computer file system. In operating systems such as CP/M and MS-DOS, where the operating system does not keep track of the file size in bytes, the end of a text file is denoted by placing one or more special characters, known as an end-of-file marker, as padding after the last line in a text file. On modern operating systems such as Microsoft Windows and Unix-like systems, text files do not contain any special EOF character, because file systems on those operating systems keep track of the file size in bytes. There are for most text files a need to have end-of-line delimiters, which are done in a few different ways depending on operating system. Some operating systems with record-orientated file systems may not use new line delimiters and will primarily store text files with lines separated as fixed or variable length records.

UTF-8 Unicode Transformation Format 8, encodes all 1,112,064 Unicode code points as 1 to 4 bytes

UTF-8 is a variable width character encoding capable of encoding all 1,112,064 valid code points in Unicode using one to four 8-bit bytes. The encoding is defined by the Unicode Standard, and was originally designed by Ken Thompson and Rob Pike. The name is derived from UnicodeTransformation Format – 8-bit.

In character encoding terminology, a code point or code position is any of the numerical values that make up the code space. Many code points represent single characters but they can also have other meanings, such as for formatting.

A poorly implemented text editor might save the replacement in UTF-8 form; the text file data will then look like this: 0x66 0xEF 0xBF 0xBD 0x72, which will be displayed in ISO-8859-1 as "f�r" (see mojibake). Since the replacement is the same for all errors this makes it impossible to recover the original character. A better (but harder to implement) design is to preserve the original bytes, including the error, and only convert to the replacement when displaying the text. This will allow the text editor to save the original byte sequence, while still showing the error indicator to the user.

Mojibake Garbled text as a result of incorrect character encoding

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

It has become increasingly common[ when? ] for software to interpret invalid UTF-8 by guessing the bytes are in another byte-based encoding such as ISO-8859-1. This allows correct display of both valid and invalid UTF-8 pasted together. If a web page uses ISO-8859-1 (or Windows-1252) but specifies the encoding as UTF-8, most web browsers used to display all non-ASCII characters as �, but newer browsers[ when? ] translate the erroneous bytes individually to characters in Windows-1252, so the replacement character is less frequently seen.

Unicode chart

Specials [1] [2] [3]
Official Unicode Consortium code chart (PDF)
 0123456789ABCDEF
U+FFFx IA 
A
 IA 
S
 IA 
T
Notes
1. ^ As of Unicode version 12.0
2. ^ Grey areas indicate non-assigned code points
3. ^ Black areas indicate noncharacters (code points that are guaranteed never to be assigned as encoded characters in the Unicode Standard)

History

The following Unicode-related documents record the purpose and process of defining specific characters in the Specials block:

Version Final code points [lower-alpha 1] Count UTC  ID L2  ID WG2  IDDocument
1.0.0U+FFFD1(to be determined)
U+FFFE..FFFF2(to be determined)
L2/01-295R Moore, Lisa (2001-11-06), "Motion 88-M2", Minutes from the UTC/L2 meeting #88
L2/01-355 N2369 (html, doc) Davis, Mark (2001-09-26), Request to allow FFFF, FFFE in UTF-8 in the text of ISO/IEC 10646
L2/02-154 N2403 Umamaheswaran, V. S. (2002-04-22), "9.3 Allowing FFFF and FFFE in UTF-8", Draft minutes of WG 2 meeting 41, Hotel Phoenix, Singapore, 2001-10-15/19
2.1U+FFFC1UTC/1995-056Sargent, Murray (1995-12-06), Recommendation to encode a WCH_EMBEDDING character
UTC/1996-002 Aliprand, Joan; Hart, Edwin; Greenfield, Steve (1996-03-05), "Embedded Objects", UTC #67 Minutes
N1365Sargent, Murray (1996-03-18), Proposal Summary - Object Replacement Character
N1353 Umamaheswaran, V. S.; Ksar, Mike (1996-06-25), "8.14", Draft minutes of WG2 Copenhagen Meeting # 30
L2/97-288 N1603 Umamaheswaran, V. S. (1997-10-24), "7.3", Unconfirmed Meeting Minutes, WG 2 Meeting # 33, Heraklion, Crete, Greece, 20 June - 4 July 1997
L2/98-004R N1681Text of ISO 10646 - AMD 18 for PDAM registration and FPDAM ballot, 1997-12-22
L2/98-070 Aliprand, Joan; Winkler, Arnold, "Additional comments regarding 2.1", Minutes of the joint UTC and L2 meeting from the meeting in Cupertino, February 25-27, 1998
L2/98-318 N1894 Revised text of 10646-1/FPDAM 18, AMENDMENT 18: Symbols and Others, 1998-10-22
3.0U+FFF9..FFFB3 L2/97-255R Aliprand, Joan (1997-12-03), "3.D Proposal for In-Line Notation (ruby)", Approved Minutes - UTC #73 & L2 #170 joint meeting, Palo Alto, CA - August 4-5, 1997
L2/98-055 Freytag, Asmus (1998-02-22), Support for Implementing Inline and Interlinear Annotations
L2/98-070 Aliprand, Joan; Winkler, Arnold, "3.C.5. Support for implementing inline and interlinear annotations", Minutes of the joint UTC and L2 meeting from the meeting in Cupertino, February 25-27, 1998
L2/98-099N1727Freytag, Asmus (1998-03-18), Support for Implementing Interlinear Annotations as used in East Asian Typography
L2/98-158 Aliprand, Joan; Winkler, Arnold (1998-05-26), "Inline and Interlinear Annotations", Draft Minutes - UTC #76 & NCITS Subgroup L2 #173 joint meeting, Tredyffrin, Pennsylvania, April 20-22, 1998
L2/98-286 N1703 Umamaheswaran, V. S.; Ksar, Mike (1998-07-02), "8.14", Unconfirmed Meeting Minutes, WG 2 Meeting #34, Redmond, WA, USA; 1998-03-16--20
L2/98-270Hiura, Hideki; Kobayashi, Tatsuo (1998-07-29), Suggestion to the inline and interlinear annotation proposal
L2/98-281R (pdf, html)Aliprand, Joan (1998-07-31), "In-Line and Interlinear Annotation (III.C.1.c)", Unconfirmed Minutes - UTC #77 & NCITS Subgroup L2 # 174 JOINT MEETING, Redmond, WA -- July 29-31, 1998
L2/98-363 N1861 Sato, T. K. (1998-09-01), Ruby markers
L2/98-372 N1884R2 (pdf, doc)Whistler, Ken; et al. (1998-09-22), Additional Characters for the UCS
L2/98-416 N1882.zip Support for Implementing Interlinear Annotations, 1998-09-23
L2/98-329 N1920 Combined PDAM registration and consideration ballot on WD for ISO/IEC 10646-1/Amd. 30, AMENDMENT 30: Additional Latin and other characters, 1998-10-28
L2/98-421R Suignard, Michel; Hiura, Hideki (1998-12-04), Notes concerning the PDAM 30 interlinear annotation characters
L2/99-010 N1903 (pdf, html, doc)Umamaheswaran, V. S. (1998-12-30), "8.2.15", Minutes of WG 2 meeting 35, London, U.K.; 1998-09-21--25
L2/98-419 (pdf, doc)Aliprand, Joan (1999-02-05), "Interlinear Annotation Characters", Approved Minutes -- UTC #78 & NCITS Subgroup L2 # 175 Joint Meeting, San Jose, CA -- December 1-4, 1998
UTC/1999-021 Duerst, Martin; Bosak, Jon (1999-06-08), W3C XML CG statement on annotation characters
L2/99-176R Moore, Lisa (1999-11-04), "W3C Liaison Statement on Annotation Characters", Minutes from the joint UTC/L2 meeting in Seattle, June 8-10, 1999
L2/01-301 Whistler, Ken (2001-08-01), "E. Indicated as "strongly discouraged" for plain text interchange", Analysis of Character Deprecation in the Unicode Standard
  1. Proposed code points and characters names may differ from final code points and names

See also

Related Research Articles

Character encoding is used to represent a repertoire of characters by some kind of encoding system. Depending on the abstraction level and context, corresponding code points and the resulting code space may be regarded as bit patterns, octets, natural numbers, electrical pulses, etc. A character encoding is used in computation, data storage, and transmission of textual data. "Character set", "character map", "codeset" and "code page" are related, but not identical, terms.

ISO/IEC 8859-1 character encoding

ISO/IEC 8859-1:1998, Information technology — 8-bit single-byte coded graphic character sets — Part 1: Latin alphabet No. 1, is part of the ISO/IEC 8859 series of ASCII-based standard character encodings, first edition published in 1987. ISO 8859-1 encodes what it refers to as "Latin alphabet no. 1", consisting of 191 characters from the Latin script. This character-encoding scheme is used throughout the Americas, Western Europe, Oceania, and much of Africa. It is also commonly used in most standard romanizations of East-Asian languages. It is the basis for most popular 8-bit character sets and the first block of characters in Unicode.

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

UTF-16 Unicode character encoding

UTF-16 is a character encoding capable of encoding all 1,112,064 valid code points of Unicode. The encoding is variable-length, as code points are encoded with one or two 16-bit code units.

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

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

ISO/IEC 8859-6:1999, Information technology — 8-bit single-byte coded graphic character sets — Part 6: Latin/Arabic alphabet, is part of the ISO/IEC 8859 series of ASCII-based standard character encodings, first edition published in 1987. It is informally referred to as Latin/Arabic. It was designed to cover Arabic. Only nominal letters are encoded, no preshaped forms of the letters, so shaping processing is required for display. It does not include the extra letters needed to write most Arabic-script languages other than Arabic itself.

ISO/IEC 2022Information technology—Character code structure and extension techniques, is an ISO standard specifying

A numeric character reference (NCR) is a common markup construct used in SGML and SGML-derived markup languages such as HTML and XML. It consists of a short sequence of characters that, in turn, represents a single character. Since WebSgml, XML and HTML 4, the code points of the Universal Character Set (UCS) of Unicode are used. NCRs are typically used in order to represent characters that are not directly encodable in a particular document. When the document is interpreted by a markup-aware reader, each NCR is treated as if it were the character it represents.

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

Universal Character Set characters Wikimedia list article

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Extended ASCII eight-bit or larger character encodings that include the standard seven-bit ASCII characters as well as others

Extended ASCII character encodings are eight-bit or larger encodings that include the standard seven-bit ASCII characters, plus additional characters. Using the term "extended ASCII" on its own is sometimes criticized, because it can be mistakenly interpreted to mean that the ASCII standard has been updated to include more than 128 characters or that the term unambiguously identifies a single encoding, neither of which is the case.

The Universal Coded Character Set (UCS) is a standard set of characters defined by the International Standard ISO/IEC 10646, Information technology — Universal Coded Character Set (UCS), which is the basis of many character encodings. The latest version contains over 136,000 abstract characters, each identified by an unambiguous name and an integer number called its code point. This ISO/IEC 10646 standard is maintained in conjunction with The Unicode Standard ("Unicode"), and they are code-for-code identical.

This article describes and classifies the Unicode characters that may validly appear in XML.

References

  1. "Unicode character database". The Unicode Standard. Retrieved 2016-07-09.
  2. "Enumerated Versions of The Unicode Standard". The Unicode Standard. Retrieved 2016-07-09.