code: function (node) {
              if (this.type == 'root' || (this.type == 'element' && !dtd.$empty[this.tagName])) {
                  if (!this.children) {
                      this.children = []
                  }
                  if(node.parentNode){
                      node.parentNode.removeChild(node);
                  }
                  for (var i = 0, ci; ci = this.children[i]; i++) {
                      if (ci === node) {
                          this.children.splice(i, 1);
                          break;
                      }
                  }
                  this.children.push(node);
                  node.parentNode = this;
                  return node;
              }
  
  
          }
docs: 在节点的子节点列表最后位置插入一个节点
  @method appendChild
  @param { UE.uNode } node 要插入的节点
  @return { UE.uNode } 返回刚插入的子节点
  @example
  ```javascript
  node.appendChild( newNode ); //在node内插入子节点newNode
  ```