docs: function _isValid (ndate, nrandom, nchecksum, id) {
    // Guard
    if (!baseURL.isValid(id)) return false;
    if (id.length !== (ndate + nrandom + nchecksum) / 6) return false;
  
    // Test
    var bits = baseURL.decode(id),
      main = bits.slice(0, bits.length - nchecksum),
      check = bits.slice(bits.length - nchecksum, bits.length);
  
    return bitString.checksum(main, nchecksum) === check;
  }