When you visit a Todo archive, the buffer is in Todo Archive mode. It displays categories just as in Todo mode, except that they only contain done items. It provides the same sequential navigation commands as Todo mode: f and b navigate between the categories of the current archive, and n and p navigate between the done items of the current archive category.
The commands t and j are also available in Todo Archive mode, and they work the same as in Todo mode, which means they can only be used to return to Todo mode: t prompt for and switch to a todo file, and with j you can only jump to a todo category. These commands exclude archives because an archive file has the same base name as the corresponding todo file, and category name completion uses only the base names, so the commands cannot know which type of file you want to visit. For this reason, there is a special command in Todo Archive mode for jumping to another archive category or visiting another archive file:
This command (todo-jump-to-archive-category) prompts for a category in the
current archive and jumps to it. Called with a prefix argument, it
prompts for another archive, then for a category in it and jumps to
that category.
None of the Todo mode editing commands are available in Todo Archive mode, since archives are meant to be static records of accomplished todo items. Should you, however, archive an item by mistake or simply change your mind about the archival status of an item, you can “unarchive” it:
Restore the done item at point to the top of the done items section of
the corresponding category in the corresponding todo file, i.e., an
unarchived item remains a done item (todo-unarchive-items). When
the last item in an archive category has been unarchived, the category
is automatically deleted from the archive. If this was the only
category in the archive, the archive file is also automatically deleted.
Since it is natural to visit an archive from the corresponding todo file, it would be convenient to easily return to the todo file when you have finished browsing the archive. If you type q to quit Todo Archive mode, this switches to the corresponding todo file and shows the todo category corresponding to the archive category you were just visiting.
The command F k (see File Editing and Todo Edit Mode) is also available in Todo Archive mode. It deletes the current archive file and prompts you whether to delete the corresponding todo file.