Space separated CSS value keywords for activating OpenType features related to numeric forms. Using the CSS keywords for feature selection is at candidate recommendation status in the CSS Fonts Module level 3 and is the spec recommended way to activate common features. Signals from content developers and font foundries indicate that the CSS font-variant-* value keywords are easier to work with and less cryptic than font-feature settings.
Docs: https://developer.mozilla.org/en/docs/Web/CSS/font-variant-numeric