public override object VisitQuestionReference(QuestionReference questionRef)
        {
            var question = _questions.Where(q => q.Name == questionRef.Name).SingleOrDefault();

            if (question != null)
            {
                StyleSet dataTypeStyleSet = _currentDataTypeStyles.GetStyleSet(question.DataType);

                StyleSet questionStyleSet = dataTypeStyleSet.GetCopy();
                questionStyleSet.OverrideStyles(questionRef.StyleAttributes);

                _questionStyles.AddStyleSet(question.Name, questionStyleSet);

                return(null);
            }
            else
            {
                throw new ApplicationException("Question not found.");
            }
        }