docs: private boolean isBorderTile(int xIndex, int yIndex, int ruleIndex) {
          for (int i = -1; i < 2; i++) {
              for (int j = -1; j < 2; j++) {
                  if (i != xIndex && j != yIndex)
                      if (ruleIndex != getRuleContainerIndex(i, j))
                          return true;
              }
          }
          return false;
      }