docs: @SuppressWarnings("unchecked")
      public Enumeration getAttributeNames() {
          HashSet<String> keys;
          synchronized (mutex) {
              keys = new HashSet<String>(window.getAttributes().keySet());
              Enumeration<String> names = super.getAttributeNames();
              while (names.hasMoreElements()) {
                  String name = (String) names.nextElement();
                  if (deleteAttributes == null || !deleteAttributes.contains(name)) {
                      keys.add(name);
                  }
              }
          }
          return new Enumerator(keys);
      }