field should typically be marked
      for translation, see the set_translation_domain() method. Optional
      with a default value of None.
    * The value to set on the radio action. Optional with a default
      value of 0. Should be specified in applications.

The value parameter specifies the radio action that should be set
active. The "changed" signal of the first radio action is connected to
the on_change callback (if specified and not None) and the accel paths
of the actions are set to <Actions>/group-name/action-name.
r½