Retrieves a list of items in a subfolder.

    The route for this endpoint is:
    ``GET /dossier/v1/folder/<fid>/subfolder/<sfid>``.

    (Temporarily, the "current user" can be set via the
    ``annotator_id`` query parameter.)

    The payload returned is a list of two element arrays. The first
    element in the array is the item's content id and the second
    element is the item's subtopic id.

def v1_subtopic_list(request, response, kvlclient, fid, sfid):
    '''Retrieves a list of items in a subfolder.

    The route for this endpoint is:
    ``GET /dossier/v1/folder/<fid>/subfolder/<sfid>``.

    (Temporarily, the "current user" can be set via the
    ``annotator_id`` query parameter.)

    The payload returned is a list of two element arrays. The first
    element in the array is the item's content id and the second
    element is the item's subtopic id.
    '''
    path = urllib.unquote(fid) + '/' + urllib.unquote(sfid)
    try:
        items = []
        for it in new_folders(kvlclient, request).list(path):
            if '@' in it.name:
                items.append(it.name.split('@'))
            else:
                items.append((it.name, None))
        return items
    except KeyError:
        response.status = 404
        return []