Specials (Unicode block)

Specials is a short Unicode block allocated at the very end of the Basic Multilingual Plane, at U+FFF0–FFFF. Of these 16 code points, five have been assigned 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.
Specials
RangeU+FFF0..U+FFFF
(16 code points)
PlaneBMP
ScriptsCommon
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]

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.

Replacement character
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" (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.

It has become increasingly common 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 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 13.0
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:

VersionFinal code points[lower-alpha 1]CountUTC IDL2 IDWG2 IDDocument
1.0.0U+FFFD1(to be determined)
U+FFFE..FFFF2(to be determined)
L2/01-295RMoore, Lisa (2001-11-06), "Motion 88-M2", Minutes from the UTC/L2 meeting #88
L2/01-355N2369 (html, doc)Davis, Mark (2001-09-26), Request to allow FFFF, FFFE in UTF-8 in the text of ISO/IEC 10646
L2/02-154N2403Umamaheswaran, 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/1996-002Aliprand, Joan; Hart, Edwin; Greenfield, Steve (1996-03-05), "Embedded Objects", UTC #67 Minutes
N1365Sargent, Murray (1996-03-18), Proposal Summary – Object Replacement Character
N1353Umamaheswaran, V. S.; Ksar, Mike (1996-06-25), "8.14", Draft minutes of WG2 Copenhagen Meeting # 30
L2/97-288N1603Umamaheswaran, V. S. (1997-10-24), "7.3", Unconfirmed Meeting Minutes, WG 2 Meeting # 33, Heraklion, Crete, Greece, 20 June – 4 July 1997
L2/98-004RN1681Text of ISO 10646 – AMD 18 for PDAM registration and FPDAM ballot, 1997-12-22
L2/98-070Aliprand, 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
L2/98-318N1894Revised text of 10646-1/FPDAM 18, AMENDMENT 18: Symbols and Others, 1998-10-22
3.0U+FFF9..FFFB3L2/97-255RAliprand, 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
L2/98-055Freytag, Asmus (1998-02-22), Support for Implementing Inline and Interlinear Annotations
L2/98-070Aliprand, 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
L2/98-158Aliprand, 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
L2/98-286N1703Umamaheswaran, 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
L2/98-363N1861Sato, T. K. (1998-09-01), Ruby markers
L2/98-372N1884R2 (pdf, doc)Whistler, Ken; et al. (1998-09-22), Additional Characters for the UCS
L2/98-416N1882.zipSupport for Implementing Interlinear Annotations, 1998-09-23
L2/98-329N1920Combined PDAM registration and consideration ballot on WD for ISO/IEC 10646-1/Amd. 30, AMENDMENT 30: Additional Latin and other characters, 1998-10-28
L2/98-421RSuignard, Michel; Hiura, Hideki (1998-12-04), Notes concerning the PDAM 30 interlinear annotation characters
L2/99-010N1903 (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/1999-021Duerst, Martin; Bosak, Jon (1999-06-08), W3C XML CG statement on annotation characters
L2/99-176RMoore, Lisa (1999-11-04), "W3C Liaison Statement on Annotation Characters", Minutes from the joint UTC/L2 meeting in Seattle, June 8-10, 1999
L2/01-301Whistler, 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
gollark: I'm sure someone else wants hatchlings.
gollark: Sorry, my slots are entirely filled.
gollark: I'm currently on bronze.
gollark: Of course, our xenowyrm overlords are better.
gollark: Nebulae: second-coolest dragon!

See also

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.
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