Duplicate characters in Unicode: Difference between revisions

Revision as of 18:54, 24 December 2024

Revision as of 19:18, 27 December 2024

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{{further|Character (computing)|Grapheme}}

Unicode aims at encoding graphemes, not individual "meanings" ("semantics") of graphemes, and not [[glyph]]s.

It is a matter of case-by-case judgement whether such characters should receive separate encoding when used in technical contexts, e.g. Greek letters used as mathematical symbols: thus, the choice to have a "[[micro-]] sign" µ separate from Greek μ, but not a "[[Mega-|Mega]] sign" separate from Latin M, was a pragmatic decision by theThe Unicode consortiumConsortium for historical reasons (namely, compatibility with [[Latin-1]], which includedincludes a micro sign). Technically µ and μ are not duplicate characters in that the consortium viewed these symbols as distinct characters (while it regarded M for "Mega" and Latin M as one and the same character).

Note that merely having different "meanings" is not sufficient grounds to split a grapheme into several characters:. Thus, the [[acute accent]] may represent word accent in Welsh or Swedish, it may express vowel quality in French, and it may express vowel length in Hungarian, Icelandic or Irish. Since all these languages are written in the same [[writing system|script]], namely [[Latin script]], the acute accent in its various meanings is considered one and the same combining diacritic character {{unichar|0301}}, and so the accented letter [[é]] is the same character in French and Hungarian. There is a separate "combining diacritic acute tone mark" at {{unichar|0341}} for the romanization of tone languages, one important difference from the acute accent being that in a language like French, the acute accent can replace the dot over the lowercase i, whereas in a language like Vietnamese, the acute tone mark is added above the dot. Diacritic signs for alphabets considered independent may be encoded separately, such as the acute ("tonos") for the Greek alphabet at {{unichar|0384}}, and for the Armenian alphabet at {{unichar|055B}}. Some Cyrillic-based alphabets (such as [[Russian alphabet|Russian]]) also use the acute accent, but there is no "Cyrillic acute" encoded separately and U+0301 should be used for Cyrillic as well as Latin (see [[Cyrillic characters in Unicode]]). The point that the same grapheme can have many "meanings" is even more obvious considering e.g. the letter [[U]], which has entirely different phonemic referents in the various languages that use it in their orthographies (English {{IPA|/juː/, /ʊ/, /ʌ/}} etc., French {{IPA|/y/}}, German {{IPA|/uː/, /u/}}, etc., not to mention various uses of [[U (disambiguation)|U as a symbol]]).

==Compatibility issues==

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===Roman numerals===

Unicode has a number of characters specifically designated as [[Roman numerals]], as part of the ''[[Number Forms'']] range from U+2160 to U+2183. For example, Roman 1988 ({{char|MCMLXXXVIII}}) could alternatively be written as {{char|ⅯⅭⅯⅬⅩⅩⅩⅧ}}. This range includes both uppercase and lowercase numerals, as well as pre-combined glyphs for numbers up to 12 ({{char|Ⅻ}} for {{char|XII}}), mainly intended for clock faces.

The pre-combined glyphs should only be used to represent the individual numbers where the use of individual glyphs is not wanted, and not to replace compounded numbers. For example, one can combine {{char|Ⅹ}} with {{char|Ⅰ}} to produce Roman numeral 11 ({{char|ⅩⅠ}}), so U+216A ({{char|Ⅺ}}) is canonically equivalent to {{char|ⅩⅠ}}. Such characters are also referred to as composite compatibility characters or decomposable compatibility characters. Such characters would not normally have been included within the Unicode standard except for compatibility with other existing encodings (see [[Unicode compatibility characters]]). The goal was to accommodate simple translation from existing encodings into Unicode. This makes translations in the opposite direction complicated because multiple Unicode characters may map to a single character in another encoding. Without the compatibility concerns the only characters necessary would be: {{Char|Ⅰ}}, {{Char|Ⅴ}}, {{Char|Ⅹ}}, {{Char|Ⅼ}}, {{Char|Ⅽ}}, {{Char|Ⅾ}}, {{Char|Ⅿ}}, {{Char|ⅰ}}, {{Char|ⅴ}}, {{Char|ⅹ}}, {{Char|ⅼ}}, {{Char|ⅽ}}, {{Char|ⅾ}}, {{Char|ⅿ}}, {{Char|ↀ}}, {{Char|ↁ}}, {{Char|ↂ}}, {{Char|ↇ}}, {{Char|ↈ}}, and {{Char|Ↄ}}, and {{char|ↄ}}; all other Roman numerals can be composed from these characters.

=== Arabic presentation forms ===

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* {{unichar|FB28}}

These characters are variants of ordinary Hebrew letters encoded for [[Justification (typesetting)|justification]] of texts written in Hebrew, such as the Torah. Unicode also encodes a stylistic variant of {{Unichar|5e2}} at {{Unichar|FB20}}.

== List ==

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* {{Unichar|FB29}}: {{Unichar|002b}}

* {{Unichar|0343|cwith=◌}}: {{Unichar|0313|cwith=◌}}

* {{Unichar|1ffd}}: {{Unichar|00B4}}

==See also==