font-variant-alternates enables simpler access to glyph alternates in fonts such as as a swashes, character-variants, ornaments and more. It provides an easier method over having to use 4-letter-codes as arguments to `font-feature-settings`. font-variant-alternates refers to the @font-feature-values at-rule to map speaking feature names to OpenType feature numbers. In the font-variant-style rule, the requested feature activation becomes easy to use and to read and allows flexible combination of font features.
As part of Interop 2022 we committed to supporting font-variant-alternates and @font-feature-values in order to reach parity with Firefox and Safari on this aspect of OpenType feature selection through CSS. The ergonomics of font-variant-alternates are better than having to know OpenType feature codes and passing them to font-feature-settings.
Samples: https://roettsch.es/montecarlo.html