public Object setLanguage(Object handle, String language) {
   if (handle instanceof Expression) {
     ((Expression) handle).setLanguage(language);
     return handle;
   }
   throw new IllegalArgumentException("handle: " + handle + " language: " + language);
 }
 public Object setBody(Object handle, String body) {
   if (handle instanceof Expression) {
     ((Expression) handle).setBody(body);
     return handle;
   }
   throw new IllegalArgumentException("handle: " + handle + " body:" + body);
 }