code: public String getDisplayName(String id, ULocale locale) {
          Map<String, Factory> m = getVisibleIDMap();
          Factory f = m.get(id);
          if (f != null) {
              return f.getDisplayName(id, locale);
          }
  
          Key key = createKey(id);
          while (key.fallback()) {
              f = m.get(key.currentID());
              if (f != null) {
                  return f.getDisplayName(id, locale);
              }
          }
  
          return null;
      }
docs: Given a visible id, return the display name in the requested locale.
  If there is no directly supported id corresponding to this id, return
  null.