src/main/java/ognl/OgnlContext.java
public Evaluation getEvaluation(int relativeIndex)
    {
        Evaluation result = null;

        if (relativeIndex <= 0) {
            result = _currentEvaluation;
            while((++relativeIndex < 0) && (result != null)) {
                result = result.getParent();
            }
        }
        return result;
    }
public Evaluation getEvaluation(int relativeIndex)
    {
        Evaluation result = null;

        if (relativeIndex <= 0) {
            result = _currentEvaluation;
            while((++relativeIndex < 0) && (result != null)) {
                result = result.getParent();
            }
        }
        return result;
    }
Returns the Evaluation at the relative index given. This should be zero or a negative number
as a relative reference back up the evaluation stack. Therefore getEvaluation(0) returns the
current Evaluation.