nonprecomposed

Nonprecomposed is a term used in typography and Unicode to describe a character that is not stored as a single precomposed code point. Instead, such characters are represented as a base letter plus one or more combining diacritical marks. In contrast, a precomposed (composed) character has a single code point that encodes both the base letter and its diacritic. Nonprecomposed sequences arise when no single code point exists for a given combination, or when text is created by input methods that separate the base and the diacritic.

Unicode and its normalization forms address these representations. Normalization forms such as NFC (Normalization Form C) and NFD (Normalization Form D) are used to convert between composed and decomposed forms. NFC tends to convert sequences into precomposed characters where such forms exist, producing a single code point for many accented letters. NFD decomposes composed characters into a base letter plus combining marks. Some characters have no precomposed form in Unicode, meaning they are inherently nonprecomposed or remain as sequences even after normalization.

Practical implications include text processing, searching, and rendering. When comparing strings, normalization helps ensure that a sequence like É (precomposed) and E + combining acute accent (nonprecomposed) are treated as equivalent. Rendering can affect ligature behavior and the alignment of combining marks, which may influence display in fonts and text engines. For developers, understanding nonprecomposed representations helps in handling input methods, data interchange, and locale-aware operations.

Example: the character É can be represented as the single code point U+00C9 (precomposed) or as E (U+0045) followed by a combining acute accent (U+0301) in a nonprecomposed form.