code: function calculateRange(range) {
          range = range || pageLoadRange;
          var currentIndex = layoutState.page - 1,
              low = currentIndex - range,
              high = currentIndex + range;
          return util.constrainRange(low, high, numPages - 1);
      }
docs: Create and return a range object (eg., { min: x, max: y })
  for the current pageLoadRange constrained to the number of pages
  @param  {int} range The range from current page
  @returns {Object}    The range object
  @private