code: function(graph, opt) {
  
          opt = opt || {};
  
          if (opt.useLocalStorage && this.length === 0 && window.localStorage) {
  
              this.reset(JSON.parse(localStorage.getItem('joint.ui.Clipboard.cells')));
          }
  
  	graph.trigger('batch:start');
  
          this.each(function(cell) {
  
              cell.unset('z');
              if ((cell instanceof joint.dia.Link) && opt.link) {
  
                  cell.set(opt.link);
              }
              
              graph.addCell(cell.toJSON());
          });
  
  	graph.trigger('batch:stop');
      }
docs: `opt.link` is attributes that will be set all links before they are added to the `graph`. This is useful for e.g. setting `z: -1` for links in order to always put them to the bottom of the paper.