void HandleTagSelectionButtonPressEvent (object sender, ButtonPressEventArgs args)
{
if (args.Event.Button == 3) {
TagPopup popup = new TagPopup ();
popup.Activate (args.Event, tag_selection_widget.TagAtPosition (args.Event.X, args.Event.Y),
tag_selection_widget.TagHighlight);
args.RetVal = true;
}
}