eys aren't
        changed, nothing happens.  If the keys are changed and the keyset
        is a builtin, function get_new_keys_name() will be called
        for input of a custom keyset name.  If no name is given, then the
        change to the keybinding will abort and no updates will be made.  If
        a custom name is entered in the prompt or if the current keyset was
        already custom (and thus didn't require a prompt), then
        idleConf.userCfg['keys'] is updated in function create_new_key_set()
        with the change to the event binding.  The item listing in bindingslist
        is updated with the new keys.  Var keybinding is also set which invokes
        the callback function, var_changed_keybinding, to add the change to
        the 'keys' or 'extensions' changes tracker based on the binding type.

        Tk Variables:
            keybinding: Action/key bindings.

        Methods:
            load_keys_list: Reload active set.
            create_new_key_set: Combine active keyset and changes.
            set_keys_type: Command for keyset_source.
            save_new_key_set: Save to idleConf.userCfg['keys'] (is function).
            deactivate_current_config: Remove keys bindings in editors.

        Widgets for KeysPage(frame):  (*) widgets bound to self
            frame_key_sets: LabelFrame
                frames[0]: Frame
                    (*)builtin_keyset_on: Radiobutton - var keyset_source
                    (*)custom_keyset_on: Radiobutton - var keyset_source
                    (*)builtinlist: DynOptionMenu - var builtin_name,
                            func keybinding_selected
                    (*)customlist: DynOptionMenu - var custom_name,
                            func keybinding_selected
                    (*)keys_message: Label
                frames[1]: Frame
                    (*)button_delete_custom_keys: Button - delete_custom_keys
                    (*)button_save_custom_keys: Button -  save_as_new_key_set
            frame_custom: LabelFrame
                frame_target: Frame
                    target_title: Label
                    scroll_target_y: Scrollbar
                    scroll_target_x: Scrollbar
                    (*)bindingslist: ListBox - on_bindingslist_select
                    (*)button_new_keys: Button - get_new_keys & ..._name
        rt