anchor.diff:  
     String toString() {
       if (!_hasValue) {
  +      var result = "Invalid arguments(s)";
         if (message != null) {
  -        return "Invalid argument(s): $message";
  +        result = "$result: $message";
         }
  -      return "Invalid argument(s)";
  +      return result;
       }
       String nameString = "";
       if (name != null) {
  
positive.code: class IndexError extends ArgumentError implements RangeError {
    /** The indexable object that [index] was not a valid index into. */
    final indexable;
    /** The invalid index. */
    final int invalidValue;
    /** The length of [indexable] at the time of the error. */
    final int length;
  
  
negative.code:    *
     * For a range from 0 to the length of something, end exclusive, use
     * [RangeError.index].
     *
     * An optional [name] can specify the argument name that has the
     * invalid value, and the [message] can override the default error
     * description.
     */
    RangeError.range(num invalidValue, this.start, this.end,
                     [String name, String message])
        : super.value(invalidValue, name,
                      (message != null) ? message : "Invalid value");
  
    /**
     * Creates a new [RangeError] stating that [index] is not a valid index
     * into [indexable].
     *
     * An optional [name] can specify the argument name that has the
     * invalid value, and the [message] can override the default error
     * description.
     *
     * The [length] is the length of [indexable] at the time of the error.
     * If `length` is omitted, it defaults to `indexable.length`.
     */
    factory RangeError.index(int index, indexable,
                             [String name,
                              String message,
                              int length]) = IndexError;
  
    String toString() {
      if (!_hasValue) return "RangeError: $message";
      String value = Error.safeToString(invalidValue);
      String explanation = "";
      if (start == null) {
        if (end != null) {
          explanation = ": Not less than or equal to $end";
        }
        // If both are null, we don't add a description of the limits.
      } else if (end == null) {
        explanation = ": Not greater than or equal to $start";
      } else if (end > start) {
        explanation = ": Not in range $start..$end, inclusive.";
      } else if (end < start) {
        explanation = ": Valid value range is empty";
      } else {
        // end == start.
        explanation = ": Only valid value is $start";
      }
      return "RangeError: $message ($value)$explanation";
    }
  }
  
  