Radio Group
A field with exactly one value, chosen from a short visible list. Use it for a discriminant — where the choice changes which fields below apply, so the reader has to see the alternatives. A closed list nobody needs to compare is a select.
Examples
A discriminant
`inline` lays the choices out in a row, which reads as one question with alternatives where a column reads as a list of unrelated settings. Every radio shares the group's name — that is what makes them exclude each other; distinct names render as radios and behave as independent toggles.
Choices that need explaining
A column, where each choice's label runs longer than a word or two. The control stays beside the label's first line rather than centred against the whole block.
Rejected, with the reason
As with the checkbox group, the message hangs off the fieldset and is announced once. Note a radio group cannot be returned to unset once a choice is made — that is the control's behaviour, so a field that may be empty needs an explicit "none" choice or a select.