FIXME: DOCS...
    Links:
       * https://developers.facebook.com/tools/explorer/

def extract(group_id, access_token, fields=None):
    '''
    FIXME: DOCS...
    Links:
       * https://developers.facebook.com/tools/explorer/

    '''
    fields = fields or ['id', 'owner', 'email', 'name', 'members']
    # TEST that fields are a subset of valid fields
    assert set(fields).issubset(VALID_FIELDS)

    get_args = {'fields': ','.join(fields),
                'access_token': access_token}
    get_args_str = '&'.join(
        ['{}={}'.format(x, y) for x, y in get_args.items()])

    base_url = 'https://graph.facebook.com/{}/?{}'.format(
        group_id, get_args_str)
    logr.debug(' LOADING URL: {}'.format(base_url))

    response = rq.get(base_url)

    # FIXME: check for errors
    # probably want to validate here somehow...?
    r_json = response.json()
    subscribers = r_json.get('members')

    return subscribers