code: function (item, index, hidden) {
          var region = item.region,
              splitter = {
                  xtype: 'bordersplitter',
                  collapseTarget: item,
                  id: item.id + '-splitter',
                  hidden: hidden,
                  canResize: item.splitterResize !== false
              },
              at = index + ((region == 'south' || region == 'east') ? 0 : 1);
  
          // remove the default fixed width or height depending on orientation:
          if (item.isHorz) {
              splitter.height = null;
          } else {
              splitter.width = null;
          }
  
          if (item.collapseMode == 'mini') {
              splitter.collapsedCls = item.collapsedCls;
          }
  
          item.splitter = this.owner.add(at, splitter);
      }
docs: ---------------------------------- Event handlers 
  Inserts the splitter for a given region. A reference to the splitter is also stored
  on the component as "splitter".
  @private