RadioButton checked doesn't change

[Sahasrara]

The checked property doesn't change if:

• You don't have a radio group
• You do have a radio group, but no "name" is specified.

[brunnerh]

Currently RadioButton is always accompanied by a RadioButtonGroup in the docs, and a group without name makes no sense.

Making checked update without a group can probably be arranged, though.
And maybe the group's name should be a required property without a default value.