anchor.diff:  
     @override
     void visitAssertInitializer(AssertInitializer node) {
  -    _recordDataForNode('AssertInitializer (condition)', node.condition);
  -    _recordDataForNode('AssertInitializer (message)', node.message);
  +    _recordDataForNode('AssertInitializer (condition)', node.condition,
  +        allowedKeywords: expressionKeywords);
  +    _recordDataForNode('AssertInitializer (message)', node.message,
  +        allowedKeywords: expressionKeywords);
       super.visitAssertInitializer(node);
     }
   
     @override
     void visitAssertStatement(AssertStatement node) {
  -    _recordDataForNode('AssertStatement (condition)', node.condition);
  -    _recordDataForNode('AssertStatement (message)', node.message);
  +    _recordDataForNode('AssertStatement (condition)', node.condition,
  +        allowedKeywords: expressionKeywords);
  +    _recordDataForNode('AssertStatement (message)', node.message,
  +        allowedKeywords: expressionKeywords);
       super.visitAssertStatement(node);
     }
   
     @override
     void visitAssignmentExpression(AssignmentExpression node) {
  -    _recordDataForNode('AssignmentExpression (rhs)', node.rightHandSide);
  +    _recordDataForNode('AssignmentExpression (rhs)', node.rightHandSide,
  +        allowedKeywords: expressionKeywords);
       var operatorType = node.operator.type;
       if (operatorType != TokenType.EQ &&
           operatorType != TokenType.QUESTION_QUESTION_EQ) {
  
positive.code: 
    @override
    void visitInterpolationExpression(InterpolationExpression node) {
      _recordDataForNode('InterpolationExpression (expression)', node.expression);
      super.visitInterpolationExpression(node);
    }
  
  
negative.code: 
    @override
    void visitPrefixExpression(PrefixExpression node) {
      _recordDataForNode('PrefixExpression (${node.operator})', node.operand,
          allowedKeywords: expressionKeywords);
      _recordTypeMatch(node.operand);
      super.visitPrefixExpression(node);
    }
  