 -- Class: <gtk-radio-tool-button>
     Derives from <gtk-toggle-tool-button>.

     This class defines the following slots:

     group
          The radio tool button whose group this button belongs to.

 -- Function: gtk-radio-tool-button-new (group <gtk-radio-group*>) =>  (ret <gtk-tool-item>)
     Creates a new <gtk-radio-tool-button>, adding it to GROUP.

     group
          An existing radio button group, or #f if you are creating a new group

     ret
          The new <gtk-radio-tool-button>

     Since 2.4

 -- Function: gtk-radio-tool-button-get-group (self <gtk-radio-tool-button>) =>  (ret <gtk-radio-group*>)
 -- Method: get-group
     Returns the radio button group BUTTON belongs to.

     button
          a <gtk-radio-tool-button>

     ret
          The group BUTTON belongs to.

     Since 2.4

 -- Function: gtk-radio-tool-button-set-group (self <gtk-radio-tool-button>) (group <gtk-radio-group*>)
 -- Method: set-group
     Adds BUTTON to GROUP, removing it from the group it belonged to before.

     button
          a <gtk-radio-tool-button>

     group
          an existing radio button group

     Since 2.4