你隻需要為radiogroup的一個輸入設定required-attribute，但你可以為所有的輸入設定。
例如：
1:
2:
3:
如果你動态生成這些單選按鈕，我建議始終添加必需的屬性，這樣你就不必擔心至少有一個輸入。
還要注意：
To avoid confusion as to whether a radio button group is required or not,authors are encouraged to specify the attribute on all the radio buttons in a group. Indeed,in general,authors are encouraged to avoid having radio button groups that do not have any initially checked controls in the first place,as this is a state that the user cannot return to,and is therefore generally considered a poor user interface.