code: public Map<List<String>, String> extractNestedDrivers(XTrace trace) {
  		return XCostDriver.instance().extractNestedValues(trace);
  	}
docs: Retrieves a map containing all cost drivers for all descending attributes
  of a trace.
  
  @see #extractNestedAmounts(XTrace)
  
  @param trace
  Trace to retrieve all cost drivers for.
  @return Map from all descending keys to cost drivers.