docs: function(x) {
      var index = null, ni = this.elements.length, ki = ni, i, nj, kj = this.elements[0].length, j;
      do { i = ki - ni;
        nj = kj;
        do { j = kj - nj;
          if (this.elements[i][j] == x) { return {i: i+1, j: j+1}; }
        } while (--nj);
      } while (--ni);
      return null;
    }