Precomposed character

A precomposed character (alternatively composite character or decomposable character) is a multi-glyph entity represented in Unicode by a single codepoint. A precomposed character may represent a letter with a diacritical mark, such as ⟨é⟩ (U+00E9 é LATIN SMALL LETTER E WITH ACUTE).

The same character can also be created using a sequence of codepoints, one for each of the glyphs that comprise the character. For example, in Unicode terms the letter ⟨é⟩ is a character that can be represented directly using U+00E9 or alternatively can be decomposed into an equivalent string of the base letter ⟨e⟩ (U+0065 e LATIN SMALL LETTER E) together with the combining form of the acute accent (U+0301 ◌́ COMBINING ACUTE ACCENT). Similarly, precomposed ligatures are precompositions of their constituent letters or graphemes – for example, the U+0133 ij LATIN SMALL LIGATURE IJ, used in Dutch.

Precomposed characters are the legacy solution for representing many special letters in various character sets. In Unicode, they were included for compatibility with early encoding systems, such as the various components of ISO 8859 and other kinds of "extended ASCII". More recent Unicode policy has been to resist creation of new precomposed characters if the character can be produced using combining forms.

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