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)
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, containing these code points:

Contents

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] An example of an internal usage of U+FFFE is the CLDR algorithm; this extended Unicode algorithm maps the noncharacter to a minimal, unique primary weight. [4]

Unicode's U+FEFFZERO WIDTH NO-BREAK SPACE 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. [5]

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 correct symbols. [6]

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.

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 [7] (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

Specials [1] [2] [3]
Official Unicode Consortium code chart (PDF)
 0123456789ABCDEF
U+FFFxIAAIASIAT�
Notes
1. ^ As of Unicode version 16.0
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:

See also

References

  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. ↑ "Unicode Technical Standard #35". Unicode Locale Data Markup Language (LDML). Retrieved 2024-08-27.
  5. ↑ "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.
  6. ↑ Wichary, Marcin (September 29, 2020). "When fonts fall". Figma. Archived from the original on 13 June 2021. Retrieved 6 June 2021.
  7. ↑ "Recommendations for OpenType Fonts (OpenType 1.7) - Typography". Microsoft Learn. Archived from the original on 19 October 2020. Retrieved 18 October 2020.
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