Definition
CSS Font Loading Module Level 3 defines FontFaceDescriptors
dictionary FontFaceDescriptors {
CSSOMString style = "normal";
CSSOMString weight = "normal";
CSSOMString stretch = "normal";
CSSOMString unicodeRange = "U+0-10FFFF";
CSSOMString featureSettings = "normal";
CSSOMString variationSettings = "normal";
CSSOMString display = "auto";
CSSOMString ascentOverride = "normal";
CSSOMString descentOverride = "normal";
CSSOMString lineGapOverride = "normal";
};