code: public static DTDElement createPlaceholder(ReaderConfig cfg, Location loc, PrefixedName name)
      {
          return new DTDElement(loc, name, null, XMLValidator.CONTENT_ALLOW_UNDEFINED,
                                cfg.willSupportNamespaces(), cfg.isXml11());
      }
docs: Method called to create a "placeholder" element definition, needed to
  contain attribute definitions.