+ "used.";
+ "used. Skips the class attribute if it is set.";
  public String globalInfo() {    return "An instance filter that assumes instances form time-series data and "      + "replaces attribute values in the current instance with the difference "      + "between the current value and the equivalent attribute attribute value "      + "of some previous (or future) instance. For instances where the time-shifted "      + "value is unknown either the instance may be dropped, or missing values "      + "used.";  }