static boolean needsQuoting(String s) {
        // Faster version of the regexp [A-Za-z0-9_][A-Za-z0-9_-]*
        if (s.isEmpty()) return true;
        if ( ! isValidFirst(s.charAt(0))) return true;
        for (int i = 1; i < s.length(); i++) {
            if (!isValidAny(s.charAt(i))) return true;
        }
        return false;
    }
Returns the single argument of the given feature name, without any quotes,
or empty if it is not a valid query, attribute or constant feature name
searchlib/src/main/java/com/yahoo/searchlib/ranking/features/FeatureNames.java