The most user-visible change was probably the simplification of the button class hierarchy. Instead of deriving GtkCheckButton from GtkToggleButton, they are now two independent widgets, and they both can be grouped to be mutually exclusive (aka as “radio group”). In this new setup, GtkRadioButton is not really needed anymore, and therefore gone.
GtkRadioButton had the following methods:
gtk_radio_button_set_group (), gtk_radio_button_get_group (), gtk_radio_button_join_group ()
Can you detail how we should now use GtkCheckButton or GtkToggleButton to replace GtkRadioButton? Which methods should we use to group them?