Specials (Unicode block)

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Specials
RangeU+FFF0..U+FFFF
(16 code points)
PlaneBMP
ScriptsCommon
Assigned5 code points
Unused9 reserved code points
2 non-characters
Unicode version history
1.0.0 (1991)1 (+1)
2.1 (1998)2 (+1)
3.0 (1999)5 (+3)
Unicode documentation
Code chart ∣ Web page
Note: [1][2]

Specials is a short Unicode block of characters 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, unrecognised, or unrepresentable character
  • U+FFFE <noncharacter-FFFE> not a character.
  • U+FFFF <noncharacter-FFFF> not a character.

U+FFFE <noncharacter-FFFE> and U+FFFF <noncharacter-FFFF> are noncharacters, meaning they are reserved but do not cause ill-formed Unicode text. Versions of the Unicode standard from 3.1.0 to 6.3.0 claimed that these characters should never be interchanged, leading some applications to use them to guess text encoding by interpreting the presence of either as a sign that the text is not Unicode. However, Corrigendum #9 later specified that noncharacters are not illegal and so this method of checking text encoding is incorrect.[3]

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.[4]

Replacement character[edit]

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 correct symbols.[5]

As an example, a text file encoded in ISO 8859-1 containing the German word für contains the bytes 0x66 0xFC 0x72. If this file is opened with a text editor that assumes the input is UTF-8, the first and third bytes are valid UTF-8 encodings of ASCII, but the second byte (0xFC) is not valid in UTF-8. The text editor could replace this byte with the replacement character to produce a valid string of Unicode code points for display, so the user sees "f�r".

A poorly implemented text editor might write out the replacement character when the user saves the file; the data in the file will then become 0x66 0xEF 0xBF 0xBD 0x72. If the file is re-opened using ISO 8859-1, it will display "f�r" (this is called mojibake). Since the replacement is the same for all errors it is impossible to recover the original character. A design that is better (but harder to implement) is to preserve the original bytes, including any errors, 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 an error indication to the user.

At one time the replacement character was often used when there was no glyph available in a font for that character, as in font substitution. 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,[6] (this browser displays 􏿾), sometimes called a 'tofu'. There is no Unicode code point for this symbol.

Thus the replacement character is now only seen for encoding errors. Some software programs translate invalid UTF-8 bytes to matching characters in Windows-1252 (since that is the most common source of these errors), so that the replacement character is never seen.

Unicode chart[edit]

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
1.^ As of Unicode version 15.1
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[edit]

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 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 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 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[edit]

References[edit]

  1. ^ "Unicode character database". The Unicode Standard. Retrieved 2023-07-26.
  2. ^ "Enumerated Versions of The Unicode Standard". The Unicode Standard. Retrieved 2023-07-26.
  3. ^ "Corrigendum #9: Clarification About Noncharacters". The Unicode Standard. Archived from the original on Jun 10, 2023. Retrieved 2023-06-07.
  4. ^ "3.8: Block-by-Block Charts" (PDF). The Unicode Standard. Version 1.0. Unicode Consortium. Archived (PDF) from the original on 2021-02-11. Retrieved 2020-09-30.
  5. ^ Wichary, Marcin (September 29, 2020). "When fonts fall". Figma. Archived from the original on 13 June 2021. Retrieved 6 June 2021.
  6. ^ "Recommendations for OpenType Fonts (OpenType 1.7) - Typography". Microsoft Learn. Archived from the original on 19 October 2020. Retrieved 18 October 2020.