How to use the cfgv.WarnAdditionalKeys function in cfgv

cfgv.ConditionalRecurse(
        'hooks', cfgv.Array(CONFIG_HOOK_DICT),
        'repo', cfgv.NotIn(LOCAL, META),
    ),
    cfgv.ConditionalRecurse(
        'hooks', cfgv.Array(MANIFEST_HOOK_DICT),
        'repo', LOCAL,
    ),
    cfgv.ConditionalRecurse(
        'hooks', cfgv.Array(META_HOOK_DICT),
        'repo', META,
    ),

    MigrateShaToRev(),
    cfgv.WarnAdditionalKeys(('repo', 'rev', 'hooks'), warn_unknown_keys_repo),
)
DEFAULT_LANGUAGE_VERSION = cfgv.Map(
    'DefaultLanguageVersion', None,
    cfgv.NoAdditionalKeys(all_languages),
    *[cfgv.Optional(x, cfgv.check_string, C.DEFAULT) for x in all_languages]
)
CONFIG_SCHEMA = cfgv.Map(
    'Config', None,

    cfgv.RequiredRecurse('repos', cfgv.Array(CONFIG_REPO_DICT)),
    cfgv.OptionalRecurse(
        'default_language_version', DEFAULT_LANGUAGE_VERSION, {},
    ),
    cfgv.Optional(
        'default_stages',
        cfgv.check_array(cfgv.check_one_of(C.STAGES)),

'default_language_version', DEFAULT_LANGUAGE_VERSION, {},
    ),
    cfgv.Optional(
        'default_stages',
        cfgv.check_array(cfgv.check_one_of(C.STAGES)),
        C.STAGES,
    ),
    cfgv.Optional('files', check_string_regex, ''),
    cfgv.Optional('exclude', check_string_regex, '^$'),
    cfgv.Optional('fail_fast', cfgv.check_bool, False),
    cfgv.Optional(
        'minimum_pre_commit_version',
        cfgv.check_and(cfgv.check_string, check_min_version),
        '0',
    ),
    cfgv.WarnAdditionalKeys(
        (
            'repos',
            'default_language_version',
            'default_stages',
            'files',
            'exclude',
            'fail_fast',
            'minimum_pre_commit_version',
        ),
        warn_unknown_keys_root,
    ),
)


class InvalidConfigError(FatalError):
    pass