anchor.diff:      throw new UnsupportedError("Not needed for pivot algorithm");    
     }
     
  -}+}
  
positive.code: part of treemap_ui.layout;
  
  typedef DataModel PivotSelectionStrategy(Iterable<DataModel> models);
  
  /**
   * Implementation of the pivot layout algorithm. For further details see
  
negative.code:  * IEEE Computer Society, pp. 73-78, 2001.
   **/
  class Pivot extends LayoutAlgorithm with LayoutUtils {
      
    PivotSelectionStrategy _selectionStrategy;
    
    Pivot([PivotSelectionStrategy selectionStrategy]) {
  