code: function getAdjacentArrayBounds(pointer, spread, length) {
          return [
              // Math.max(0, pointer - spread),
              Math.max(0, pointer),
              Math.min(length - 1, pointer + spread)
          ]
      }
docs: [getAdjacentArrayBounds retuns existing adjacent lower and upper column bounds]
  @param  {[int]} pointer [current index]
  @param  {[int]} spread  [distance from index]
  @param  {[int]} length     [total length]
  @return {[array]}         [0] lower bound, [1] upper bound