# Notebook tab has been clicked (receives numeric page_num), but *NOT* yet changed (visually).
    def channel_switch(self, notebook, page, page_num=0, *args):
        self.current_channel = notebook.get_menu_label_text(notebook.get_nth_page(page_num))
        __print__(dbg.UI, "main.channel_switch():", "set current_channel :=", self.current_channel)
        self.update_title()
        
        # if first selected, load current category
        __print__(dbg.STAT, "TRY", "main.channel_switch(): ", self.current_channel + ".first_show()")
        try: self.channel().first_show()
        except: __print__(dbg.INIT, ".first_show() initialization error")

    # Invoked from the menu instead, uses module name instead of numeric tab id
    def channel_switch_by_name(self, name):
        self.notebook_channels.set_current_page(self.channel_names.index(name))

    # Mirror selected channel tab into main window title
    def update_title(self):