code: function chartMouseDown(e) {
  
                  if ((e.button && e.button === 1) || (e.which && e.which === 2)) {
                      e.preventDefault();
                      var offsets = plot.offset();
                      plot.getPlaceholder().append('<div id="plot-highlight-div"></div>').bind('mousemove', middleMouseMove);
                      $('#plot-highlight-div').bind('mouseup', chartMouseUp);
                      that.highlightContainer.highlighting = true;
                      that.highlightContainer.start = e.clientX;
                      return;
                  }
  
                  that.previousXPosition = e.clientX;
                  that.previousYPosition = e.clientY;
  
                  if (e.shiftKey) {
                      that.panType = 'vertical';
                      plot.getPlaceholder().bind('mousemove', vertPanChart);
                  }
                  else {
                      that.panType = 'horizontal';
                      plot.getPlaceholder().bind('mousemove', horPanChart);
                  }
              }
docs: ************************************************************
  Event Functions
  ************************************************************