code: function () {
              var Clazz = this.constructor;
              var node = new Clazz(this.value, this.engine);
  
              /* eslint-disable no-redeclare */
              for (var i = 0, l = this.children.length; i < l; i++) {
                  node.addChild(this.children[i].clone());
              }
  
              for (var i = 0, l = this.cloneProps.length; i < l; i++) {
                  var prop = this.cloneProps[i];
                  node[prop] = this[prop];
              }
              /* eslint-enable no-redeclare */
  
              return node;
          }
docs: 复制节点的方法
  
  @return {Command} 节点复制对象