OpenType variable fonts integration in the layout engine affects at least the following aspects: 1) Axis value assignments from font-variation-settings 2) Integration of variable fonts axis parameters into layout operations 3) Font matching for: * Matching based on canonical scalable axes such as width or weight or optical sizing. * Matching named instances 4) Feature resolution of CSS props, feature-settings and variation settings
Docs: https://medium.com/@tiro/https-medium-com-tiro-introducing-opentype-variable-fonts-12ba6cd2369 https://www.microsoft.com/en-us/Typography/OpenTypeSpecification.aspx
Samples: https://jsfiddle.net/k6pkvj66/1/