必需属性未在select元素上验证

Question

出于某种原因，required属性无效。我哪里出错了？

我已经尝试过另一个<option>空白value

<form action="">
    <select required>
        <optgroup label="test">
            <option value="">choose</option>
            <option value="red">red</option>
            <option value="yellow">yellow</option>
            <option value="green">green</option>
            <option value="grey">grey</option>
        </optgroup>
    </select>
    <input type="submit">
</form>

Answer 1

没有optgroup DEMO

<form method="POST" action="">
    <select required>
      <option value="">choose</option>
      <option value="red">red</option>
      <option value="yellow">yellow</option>
      <option value="green">green</option>
      <option value="grey">grey</option>
    </select>
    <input type="submit">
</form>

无论如何，浏览器中的required attribute支持不足