How to use the cfgv.ConditionalOptional function in cfgv

('name', 'identity'),
            ('verbose', True),
            ('entry', _entry('identity')),
        ),
    ),
)

META_HOOK_DICT = cfgv.Map(
    'Hook', 'id',
    cfgv.Required('id', cfgv.check_string),
    cfgv.Required('id', cfgv.check_one_of(tuple(k for k, _ in _meta))),
    # language must be system
    cfgv.Optional('language', cfgv.check_one_of({'system'}), 'system'),
    *([
        # default to the hook definition for the meta hooks
        cfgv.ConditionalOptional(key, cfgv.check_any, value, 'id', hook_id)
        for hook_id, values in _meta
        for key, value in values
    ] + [
        # default to the "manifest" parsing
        cfgv.OptionalNoDefault(item.key, item.check_fn)
        # these will always be defaulted above
        if item.key in {'name', 'language', 'entry'} else
        item
        for item in MANIFEST_HOOK_DICT.items
    ])
)
CONFIG_HOOK_DICT = cfgv.Map(
    'Hook', 'id',

    cfgv.Required('id', cfgv.check_string),