Most modern variable fonts ship both proportional numerals (each digit takes only its visual width) and tabular numerals (every digit is the same width as a digit-9). Tabular nums are required wherever numbers stack vertically — invoices, pricing tables, data dashboards — because proportional widths produce jittery columns. AI2 Design's `accessibilityRules` and `typographyRules` mark tabular-nums as mandatory on aligned numerics.
Glossary · typography
Tabular Numerals
A font feature (`font-variant-numeric: tabular-nums`) that forces every digit to occupy the same width — essential for aligned columns.
External reference
MDN — font-variant-numericCatalogued examples
2 catalogued sites demonstrate tabular numerals in production.