Space separated CSS value keywords for activating OpenType features related to small-caps, all-small-caps, etc. 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-caps