static InputStream getDoctypeDefinition(Cons doctype) {
    { String definition = ((StringWrapper)(((Cons)(doctype.rest.value)).rest.value)).wrapperValue;

      if (Stella.internalDtdDefinitionP(definition)) {
        return (InputStringStream.newInputStringStream(Native.string_subsequence(definition, 1, definition.length() - 2)));
      }
      else {
        return (null);
      }
    }
  }