Baseplusdiacritics

Baseplusdiacritics is a term used in typography and digital text processing to describe representations where a base character is augmented by one or more diacritical marks to modify its value. In practice, this concept covers both precomposed characters that already include diacritics (for example é) and sequences where a base letter is followed by one or more combining diacritical marks (for example e followed by a combining acute accent).

In Unicode and related text standards, diacritics are often represented as combining marks. These marks sit on top of or below the base character and may be stacked or arranged in a specific order. Common combining marks live in blocks such as the combining diacritical marks range, and additional marks exist in other ranges. Normalization forms, notably NFC and NFD, govern how base letters and diacritics are stored and compared: NFC prefers a single precomposed code point when available, while NFD expands to a base letter plus combining marks. This affects data processing, search, and rendering.

Rendering baseplusdiacritics relies on fonts that support both the base characters and the combining marks, as well as proper diacritic placement rules. The order and stacking of multiple diacritics can influence appearance and legibility, and some languages require specific sequences of marks for correct representation.

Applications and challenges include text normalization for search and comparison, input method design, and typography. Canonical equivalence means that different representations (composed versus decomposed) can convey the same visible text, which must be handled consistently in software and fonts.

Examples include é (base e with acute), ö (o with diaeresis), and ñ (n with tilde), among many other combinations used across languages.