You may try the evaluateXPath method of MbElement. Use its overload with
string expression for easy setup otherwise you can set up MbXPath first. Like this.
It might return Boolean, Double, String or List of MbElement according to the documentation. In the case where there are multiple BASE, ORDER, or DETAILS, it would probably return a List. In that case, use iterator to iterate through the returned list. Experimenting it a bit.