docs: function lookup(locale, format, obj) {
    if (!locale) throw new Error('missing required "locale" parameter');
    locale = locale.toLowerCase().replace('-', '_');
    format = format || 'cardinal';
    var p = obj[format];
    if (!p) throw new Error('unsupported format "' + format + '"');
    var fn = p[locale] || p[locale.split('_')[0]];
    if (fn) return fn;
  
    throw new Error('unsupported locale "' + locale + '"');
  }