markdrift

Markdrift is a term used in typography and digital rendering to describe the observed misalignment of diacritic marks relative to their base letters under certain conditions. The term combines mark, referring to diacritical symbols, and drift, referring to unintended movement. It is discussed in the context of rendering quality and font design rather than as a formal typographic category.

Causes include font hinting and glyph substitution when combining marks attach to base letters, subpixel rendering, complex script shaping, and differences between rendering engines. Small font sizes and high-contrast screens can exacerbate drift, especially for languages that rely heavily on combining marks.

Measurement typically involves comparing the anchor positions of diacritics to their bases across a test suite of fonts and sizes, or using automated tests to detect deviations from expected baselines. Some researchers distinguish between drift that is perceptible to readers and drift that remains within tolerances of a given font system.

Mitigation strategies include using robust fonts with explicit diacritic anchors, preferring precomposed characters when appropriate, ensuring consistent font-family usage, enabling reliable diacritic placement features in shaping engines, and testing across platforms. Font designers may adjust metrics or provide fallback mechanisms to maintain alignment.

Although not universally recognized as a formal phenomenon, markdrift is discussed in font design and rendering optimization contexts to improve legibility and consistency, particularly for multilingual typesetting and user interface typography.

See also: diacritic placement, combining marks, font hinting, ligatures, anchor-based diacritics.