form
form 안의 button은 자동으로 submit 버튼이 된다.
<form>
<button>I'm submit button</button>
</form><form>
<button type="submit">I'm submit button</button>
</form><form>
<button type="button">I'm just button</button>
</form><form>
<button>I'm submit button</button>
</form><form>
<button type="submit">I'm submit button</button>
</form><form>
<button type="button">I'm just button</button>
</form>