I'm
          using gtkmm to build a UI. The task I'm trying to accomplish
          is constructing a radio button from an action that is already
          part of a menu and a toolbar. I'd like the new button to proxy
          for the existing action.
        One
          likely candidate is Gtk::Action::create_tool_item(). Its
          documentation states:
        
          Deprecated:
            3.10: Use a Gtk::ToolItem and associate it with a Action
            using Gtk::Actionable::set_action_name() instead
        
        So,
          I'd expect that ToolItem and by inheritance RadioToolButton
          would implment this interface. In gtkmm-3.12 it does not and
          the stable documentation reflects this as well.
        However,
          the C library gtk-3.0 RadioToolButton does implement this
          interface. So, my question is this.
        Should
            gtkmm Gtk::RadioToolButton implement Gtk::Actionable? Is the
            absence of this int erface an oversight, or is there another
            way that the features of Actionable are supported?