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
1.0.0 (1991)1 (+1)
2.1 (1998)2 (+1)
3.0 (1999)5 (+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 have been assigned since Unicode 3.0:

Contents

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.

Its block name in Unicode 1.0 was Special. [3]

Replacement character

Replacement character Replacement character.svg
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 to indicate problems when a system is unable to render a stream of data to a correct symbol. [4] It is usually seen when the data is invalid 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 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 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" (this is called 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.

At one time the replacement character was often used when there was no glyph available in a font for that character. However most modern text rendering systems instead use a font's .notdef character, which in most cases is an empty box (or "?" or "X" in a box [5] ), sometimes called a "tofu" (this browser displays 􏿾). There is no Unicode code point for this symbol.

Thus the replacement character is now only seen for encoding errors, such as invalid UTF-8. Some software attempts 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)
 0123456789ABCDEF
U+FFFx IA 
A
 IA 
S
 IA 
T
Notes
1. ^ As of Unicode version 14.0
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

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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.
  3. "3.8: Block-by-Block Charts" (PDF). The Unicode Standard. version 1.0. Unicode Consortium.
  4. Wichary, Marcin. "When Fonts Fall". Figma. Retrieved 6 June 2021.
  5. "Recommendations for OpenType Fonts (OpenType 1.7) - Typography". docs.microsoft.com. Retrieved 18 October 2020.