docs: function shouldLoadPage(index) {
          var page = pages[index];
  
          // does the page exist?
          if (page) {
  
              // within page load range?
              if (indexInRange(index)) {
                  return true;
              }
  
              // is it visible?
              if (pageIsVisible(index)) {
                  return true;
              }
          }
  
          return false;
      }