code: private String extractCurrencyPrivate(XAttributable element) {
  		XAttribute attribute = element.getAttributes().get(KEY_CURRENCY);
  		if (attribute == null) {
  			return null;
  		} else {
  			return ((XAttributeLiteral) attribute).getValue();
  		}
  	}
docs: /*
  Retrieves the cost currency for an element, if set by this extension's
  currency attribute.
  
  @param event Element to retrieve currency for.
  
  @return The requested cost currency.