### for debug
<cn>
#### 基本
默认选中第一项。
</cn>

<us>
#### Nest
Default activate first tab.
</us>

```html
<template>
<div>
  <a-select style="width: 200px" v-model="parentPos">
      <a-select-option v-for="pos in positionList" :key="pos" :value="pos">Parent - {{pos}}</a-select-option>
  </a-select>

  <a-select style="width: 200px" v-model="childPos">
    <a-select-option v-for="pos in positionList" :key="pos" :value="pos">Child - {{pos}}</a-select-option>
  </a-select>

  <a-select style="width: 200px" v-model="parentType">
    <a-select-option value="line">Parent - line</a-select-option>
    <a-select-option value="card">Parent - card</a-select-option>
  </a-select>

  <a-select style="width: 200px" v-model="childType">
    <a-select-option value="line">Child - line</a-select-option>
    <a-select-option value="card">Child - card</a-select-option>
  </a-select>

  <a-tabs defaultActiveKey="1" :tabPosition="parentPos" :type="parentType">
    <a-tab-pane tab="Tab 1" key="1">
      <a-tabs :defaultActiveKey="1" :tabPosition="childPos" :type="childType" style="height: 300px">
        <a-tab-pane v-for="key in list" :tab="`Tab ${key}`" :key="key">TTTT {{key}}</a-tab-pane>
      </a-tabs>
    </a-tab-pane>
    <a-tab-pane tab="Tab 2" key="2">Content of Tab Pane 2</a-tab-pane>
  </a-tabs>
</div>
</template>
<script>
const positionList = ['left', 'right', 'top', 'bottom'];
const list = new Array(20).fill().map((_, index) => index);
export default {
  data () {
    return {
      positionList,
      list,
      parentPos: undefined,
      childPos: undefined,
      parentType: undefined,
      childType: undefined,
    }
  },
}
</script>
```
