Validating radio buttons and checkboxes
As explained in the core API feature on checkboxes and radio buttons, radio buttons and checkboxes can be validated simply by adding validators only to one element in the group. In the HTML extension, this means that you can add validation class names to only one element. This also goes for customizing field names, error messages and so on.
Example
The following is the example from the core API feature mentioned above revisited, now with validation through HTML. Refer to the original description for a thourough description.