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