      *  Specifies the name of the group to which this FxRadioButton control belongs, or 
      *  specifies the value of the <code>id</code> property of a FxRadioButtonGroup control
      *  if this FxRadioButton is part of a group defined by a FxRadioButtonGroup control.
+     *  All radio buttons with the same groupName will be in the same tab group.
+     *  All radio buttons in the group must have the same parent.  
      *
-     *  @default "undefined"
+     *  @default "radioButton"
+     *  @see #group
+     * 
+     *  @throws ArgumentError If the radio button has a different parent than
+     *  the other radio buttons already in the group.
      */
     public function get groupName():String
     {

    /**
     *  @private
     */
    mx_internal function removeFromGroup():void
    {        
        // If the radio button was in a group, remove it.
        this.dispatchEvent(new Event(Event.REMOVED));

        if (!enabled || selected)
            return; // prevent a selected button from dispatching "click"

        if (!mx_internal::radioButtonGroup)
            addToGroup();

        // Must call super.clickHandler() before setting
        // the group's selection.
        super.onClick(event);

        group.mx_internal::setSelection(this);

        // Dispatch an itemClick event from the FxRadioButtonGroup.
        var itemClickEvent:ItemClickEvent =
            new ItemClickEvent(ItemClickEvent.ITEM_CLICK);
        itemClickEvent.label = label;
        itemClickEvent.index = mx_internal::indexNumber;
        itemClickEvent.relatedObject = this;
        itemClickEvent.item = value;
        group.dispatchEvent(itemClickEvent);
