anchor.diff:    result := TFhirIndex(Inherited Clone);
   end;
   
  +destructor TFhirIndex.Destroy;
  +begin
  +  FExpression.Free;
  +  inherited;
  +end;
  +
   function TFhirIndex.Link: TFhirIndex;
   begin
     result := TFhirIndex(Inherited Link);
  +end;
  +
  +procedure TFhirIndex.SetExpression(const Value: TFHIRPathExpressionNode);
  +begin
  +  FExpression.Free;
  +  FExpression := Value;
   end;
   
   function TFhirIndex.specifiedTarget: String;
  
positive.code:     FPath : String;
      FUsage : TFhirSearchXpathUsageEnum;
      FMapping : String;
    public
      function Link : TFhirIndex; Overload;
      function Clone : TFhirIndex; Overload;
      procedure Assign(source : TAdvObject); Override;
  
negative.code:     Property Path : String read FPath;
      Property Usage : TFhirSearchXpathUsageEnum read FUsage;
      Property Mapping : String read FMapping write FMapping;
      property expression : TFHIRPathExpressionNode read FExpression write SetExpression;
  
      function specifiedTarget : String;
    end;
  