How to use the "required" attribute with a "radio" input field

Question

I am just wondering how to use the new HTML5 input attribute "required" in the right way on radio buttons. Does every radio button field need the attribute like below or is it sufficient if only one field gets it?

<input type="radio" name="color" value="black" required="required" />
<input type="radio" name="color" value="white" required="required" />

Answer 1

TL;DR: Set the required attribute for at least one input of the radio group.

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Setting required for all inputs is more clear, but not necessary (unless dynamically generating radio-buttons).

To group radio buttons they must all have the same name value. This allows only one to be selected at a time and applies required to the whole group.

<form>
  Select Gender:<br>

  <label>
    <input type="radio" name="gender" value="male" required>
    Male
  </label><br>

  <label>
    <input type="radio" name="gender" value="female">
    Female
  </label><br>

  <label>
    <input type="radio" name="gender" value="other">
    Other
  </label><br>

  <input type="submit">
</form>

Also take note of:

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.

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