code: public static ElementSelector xor(final ElementSelector es1,
                                        final ElementSelector es2) {
          if (es1 == null || es2 == null) {
              throw new IllegalArgumentException(SELECTORS_MUST_NOT_BE_NULL);
          }
          return new ElementSelector() {
              @Override
              public boolean canBeCompared(Element controlElement,
                                           Element testElement) {
                  return es1.canBeCompared(controlElement, testElement)
                      ^ es2.canBeCompared(controlElement, testElement);
              }
          };
      }
docs: Accepts two elements if exactly on of the given ElementSelectors does.