code: public static ElementSelector not(final ElementSelector es) {
          if (es == null) {
              throw new IllegalArgumentException("es must not be null");
          }
          return new ElementSelector() {
              @Override
              public boolean canBeCompared(Element controlElement,
                                           Element testElement) {
                  return !es.canBeCompared(controlElement, testElement);
              }
          };
      }
docs: Negates another ElementSelector.