fontfeature

Fontfeature, in typography, refers to the set of optional glyph shapes and arrangements that a font can provide beyond its basic character shapes. These features are part of how OpenType fonts encode advanced typography and are implemented through substitution and positioning rules that affect how characters are rendered together.

In OpenType, font features are defined in the font’s GSUB (glyph substitution) and GPOS (glyph positioning) tables and are identified by four-letter feature tags. Common examples include liga (standard ligatures), dlig (discretionary ligatures), hlig (historical ligatures), calt (contextual alternates), and salt (stylistic alternatives). Other tag families cover small capitals (smcp), alternates (ss01–ss20), numerals (onum for oldstyle, lnum for lining, tnum for tabular), subs (subscript), sups (superscript), ordn (ordinal forms), and frac (fractional forms). Fonts may expose many such features, and applications decide which to enable.

Usage in software typically involves a feature-selection mechanism. In CSS, the font-feature-settings property or the font-variant-ligatures family of properties lets developers enable or disable specific features, for example by referencing the 'liga' or 'ss01' tags. Other typesetting systems provide similar controls, often with user-facing options to turn features on or off.

Support and behavior vary across fonts and platforms. Not all fonts expose the same features, and rendering engines may apply defaults or ignore certain features. When features are supported, they can improve readability and typographic personality; when not, the text falls back to the font’s basic glyphs.