Index: frontend/node_modules/unicode-match-property-value-ecmascript/index.js
===================================================================
--- frontend/node_modules/unicode-match-property-value-ecmascript/index.js	(revision 9af201e94b5a79beb92a30858fc54de4bc3b9449)
+++ frontend/node_modules/unicode-match-property-value-ecmascript/index.js	(revision 9af201e94b5a79beb92a30858fc54de4bc3b9449)
@@ -0,0 +1,19 @@
+'use strict';
+
+const propertyToValueAliases = require('./data/mappings.js');
+
+const matchPropertyValue = function(property, value) {
+	const aliasToValue = propertyToValueAliases.get(property);
+	if (!aliasToValue) {
+		throw new Error(`Unknown property \`${ property }\`.`);
+	}
+	const canonicalValue = aliasToValue.get(value);
+	if (canonicalValue) {
+		return canonicalValue;
+	}
+	throw new Error(
+		`Unknown value \`${ value }\` for property \`${ property }\`.`
+	);
+};
+
+module.exports = matchPropertyValue;