The XML interface works exactly like the Booking Engine when a multi day booking has different rates per day. The saved booking simply has the Daily Rate and one can then deduce the Average Daily Rate (ADR) by adding all day's rates and dividing by the number of nights.

For example, if your rate is $10 for the first night, $20 for the second night, and $30 for the third night, the Average Daily Rate (ADR) saved for a 3-day stay would be 10+20+30=60. 60/3=$20. Thus the Average Daily Rate (ADR) is $20.