code: void setDefaultArg0Element(XmlModelWriter xw, String displayName, boolean displayNameIsResource, Element element)
      {
          Element defaultArg0Element = getArgElement(xw, element, 0, null, _rules.size() > 0);
  
          if (defaultArg0Element != null)
          {
              setElementAttribute(defaultArg0Element, "key", displayName);
              setElementAttribute(defaultArg0Element, "resource", Boolean.toString(displayNameIsResource));
              defaultArg0Element.removeAttribute("bundle");
          }
      }
docs: Find or create a default arg 0 element not associated with a specific rule and set it to the display name.