code: public Bits xorSet(Bits xs) {
          Assert.check(currentState != BitsState.UNKNOWN);
          sizeTo(xs.bits.length);
          for (int i = 0; i < xs.bits.length; i++) {
              bits[i] = bits[i] ^ xs.bits[i];
          }
          currentState = BitsState.NORMAL;
          return this;
      }
docs: this set = this set ^ xs.