code: function(items) {
              var hasRelativePositioning = hasNumberProperty(items, 'relativePosition');
  
              for(var i = 0; i < items.length; i++) {
                  if(i == items.length - 1)
                      items[i].diffWithNextRelativePos = undefined;
                  else
                      items[i].diffWithNextRelativePos = items[i + 1].relativePosition - items[i].relativePosition;
              }
          }
docs: Method that calculates relativePosition difference with next item