Specials (Unicode block)
Unicode block (U+FFF0-FFFF) containing a few interlinear annotation controls and replacement characters, as well as two special code points permanently reserved as non-characters at end of their code plane From Wikipedia, the free encyclopedia
Specials is a short Unicode block of characters put at the very end of the Basic Multilingual Plane, at U+FFF0–FFFF. Of these 16 code points, five have been used since Unicode 3.0:
- U+FFF9 INTERLINEAR ANNOTATION ANCHOR, marks start of annotated text
- U+FFFA INTERLINEAR ANNOTATION SEPARATOR, marks start of annotating character(s)
- U+FFFB INTERLINEAR ANNOTATION TERMINATOR, marks end of annotation block
- U+FFFC  OBJECT REPLACEMENT CHARACTER, placeholder in the text for another unspecified object, for example in a compound document.
- U+FFFD � REPLACEMENT CHARACTER used to replace an unknown, unrecognized, or unrepresentable character
- U+FFFE <noncharacter-FFFE> not a character.
- U+FFFF <noncharacter-FFFF> not a character.
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FFFE and FFFF are not unused in the usual way, but guaranteed not to be Unicode characters at all. They can be used to guess a text's scheme, since any text using these is not a correctly encoded Unicode text. Unicode's U+FEFF BYTE ORDER MARK character can be put at the start of a Unicode text to signal its endianness: a program reading such a text and finding 0xFFFE would then know that it should switch the byte order for all the following characters.
Its block name in Unicode 1.0 was Special.[3]
Replacement character
The replacement character (�) (often displayed as a black rhombus with a white question mark) is a symbol found in the Unicode standard at code point U+FFFD in the Specials table. It is used for problems when something is unable to render a stream of data to a correct symbol.[4] It is usually seen when the data is not valid and does not match any character:
Consider a text file containing the German word für (meaning 'for') in the ISO-8859-1 encoding (0x66 0xFC 0x72). This file is now opened with a text editor that thinks that 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. So, a text editor could replace this byte with the replacement character symbol to make a valid string of Unicode code points. The whole string now looks like this: "f�r".
A poorly made text editor might save the replacement character in UTF-8, and 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" (this is called mojibake). Since the replacement is the same for all errors this makes it impossible to get the first character. A better (but harder to make) way is to keep 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 to the user.
At one time the replacement character was used a lot when there was no glyph that can be used in a font for that character. However, most new text rendering systems instead use a font's .notdef character, which most times is an empty box (or "?" or "X" in a box[5]), sometimes called a "tofu" (this browser displays ). There is no Unicode point for this symbol.
So, the replacement character is now only seen for encoding errors, such as invalid UTF-8. Some software tries to hide this by translating the bytes of invalid UTF-8 to matching characters in Windows-1252 (since that is the most likely source of these errors), so that the replacement character is never seen.
Unicode chart
| Specials[1][2][3] Official Unicode Consortium code chart (PDF) | ||||||||||||||||
| 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | A | B | C | D | E | F | |
| U+FFFx | IAA | IAS | IAT |  | � | |||||||||||
| Notes | ||||||||||||||||
History
The following Unicode-related documents record the purpose and process of defining specific characters in the Specials block:
| Version | Final code points[a] | Count | UTC ID | L2 ID | WG2 ID | Document |
|---|---|---|---|---|---|---|
| 1.0.0 | U+FFFD | 1 | (to be determined) | |||
| U+FFFE..FFFF | 2 | (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 | ||||
| 2.1 | U+FFFC | 1 | UTC/1995-056 | Sargent, 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 | |||||
| N1365 | Sargent, Murray (1996-03-18), Proposal Summary – Object Replacement Character | |||||
| N1353 Archived 2017-02-22 at the Wayback Machine | 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 | N1681 | Text 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 | ||||
| 3.0 | U+FFF9..FFFB | 3 | 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 | |||||
| L2/98-099 | N1727 | Freytag, 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 Archived 2020-10-03 at the Wayback Machine | Umamaheswaran, V. S.; Ksar, Mike (1998-07-02), "8.14", Unconfirmed Meeting Minutes, WG 2 Meeting #34, Redmond, WA, USA; 1998-03-16--20 | ||||
| L2/98-270 | Hiura, 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 Archived 2020-10-02 at the Wayback Machine | 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 | |||||
Related pages
- Unicode control characters
References
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