code: public Reference referenceAt(T property, int position)
      {
          return getEvaluator().referenceAt(getRawProperty(property), position, getRetriever());
      }
docs: Retrieve the reference to another property from within the value of the
  given property at the given position. If such a reference does not exist,
  the result of this method will be <code>null</code>.
  
  @param property
  the property to search for the requested reference
  @param position
  the position to check for a reference
  @return the appropriate reference if one exists; <code>null</code>
  otherwise