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