Saxon

FeatureData.featureList has the required information, it should be possible to change CommandLineOptions.featureKeys() to something like

public static String featureKeys(String edition) {
        final int index = "http://saxon.sf.net/feature/".length();
        StringBuilder sb = new StringBuilder();
        for (String name : FeatureIndex.getNames()) {
            if (FeatureIndex.getData(name).editions.contains(edition)) {
               sb.append("\n  ").append(name.substring(index));
            }
        }
        return sb.toString();
    }