anchor.diff:    }
   }
   
  +/// A material design linear progress indicator.
  +///
  +/// A widget that shows progress along a line. There are two kinds of linear
  +/// progress indicators:
  +///
  +///  * _Determinate_. Determinate progress indicators have a specific value at
  +///    each point in time, and the value should increase monotonically from 0.0
  +///    to 1.0, at which time the indicator is complete. To create a determinate
  +///    progress indicator, use a non-null [value] between 0.0 and 1.0.
  +///  * _Indeterminate_. Indeterminate progress indicators do not have a specific
  +///    value at each point in time and instead indicate that progress is being
  +///    made without indicating how much progress remains. To create an
  +///    indeterminate progress indicator, use a null [value].
  +///
  +/// See also:
  +///
  +///  * [CircularProgressIndicator]
  +///  * <https://www.google.com/design/spec/components/progress-activity.html#progress-activity-types-of-indicators>
   class LinearProgressIndicator extends ProgressIndicator {
  +  /// Creates a linear progress indicator.
  +  ///
  +  /// The [value] argument can be either null (corresponding to an indeterminate
  +  /// progress indcator) or non-null (corresponding to a determinate progress
  +  /// indicator). See [value] for details.
     LinearProgressIndicator({
       Key key,
       double value
  
positive.code: 
  // TODO(hansmuller): implement the support for buffer indicator
  
  abstract class ProgressIndicator extends StatefulWidget {
    ProgressIndicator({
      Key key,
      this.value
    }) : super(key: key);
  
    final double value; // Null for non-determinate progress indicator.
  
    Color _getBackgroundColor(BuildContext context) => Theme.of(context).backgroundColor;
    Color _getValueColor(BuildContext context) => Theme.of(context).primaryColor;
  
negative.code:   }
  }
  
  /// A material design circular progress indicator.
  ///
  /// A widget that shows progress along a circle. There are two kinds of circular
  /// progress indicators:
  ///
  ///  * _Determinate_. Determinate progress indicators have a specific value at
  ///    each point in time, and the value should increase monotonically from 0.0
  ///    to 1.0, at which time the indicator is complete. To create a determinate
  ///    progress indicator, use a non-null [value] between 0.0 and 1.0.
  ///  * _Indeterminate_. Indeterminate progress indicators do not have a specific
  ///    value at each point in time and instead indicate that progress is being
  ///    made without indicating how much progress remains. To create an
  ///    indeterminate progress indicator, use a null [value].
  ///
  /// See also:
  ///
  ///  * [LinearProgressIndicator]
  ///  * <https://www.google.com/design/spec/components/progress-activity.html#progress-activity-types-of-indicators>
  class CircularProgressIndicator extends ProgressIndicator {
    /// Creates a circular progress indicator.
    ///
    /// The [value] argument can be either null (corresponding to an indeterminate
    /// progress indcator) or non-null (corresponding to a determinate progress
    /// indicator). See [value] for details.
    CircularProgressIndicator({
      Key key,
      double value
  