docs: function(subtree, method, onComplete) {
              if(method == 'replot') {
                  this.op.sum(subtree, $.extend({ type: 'replot' }, onComplete || {}));
              } else if (method == 'animate') {
                  this.op.sum(subtree, $.extend({ type: 'fade:seq' }, onComplete || {}));
              }
          }