# cache list, to determine if a PLS url is bookmarked
    urls = []

    def gui(self, parent):
        parent.notebook_channels.set_menu_label_text(parent.v_bookmarks, "bookmarks")
        GenericChannel.gui(self, parent)
        uikit.tree_column(self.gtk_cat, "Group")

    # this channel does not actually retrieve/parse data from anywhere
    def update_categories(self):
        pass
        
    # but category sub-plugins might provide a hook
    category_plugins = {}