docs: function flattenOptionChildren(children) {
      let content = '';
      // 忽略掉里面的元素节点
      Children.forEach(children, function(child) {
          if (child == null) {
              return;
          }
          if (typeof child === 'string' || typeof child === 'number') {
              content += child;
          }
      });
      return content;
  }