code: function getSequence() {
      var mod = ++seq % 16
  
      // reset counter
      if (seq > 0xffffff)
          seq = mod = 0
  
      // If counter is divisible by 16 then
      // the sequence prefix should be regenerated.
      // Otherwise only the last digit changed,
      // so we don't need to update the prefix.
      if (!mod)
          seqpref = pad(~~(seq / 16), 5, 16)
  
      return seqpref + digits[ mod ]
  }
docs: Increase or reset sequence counter and recalculate prefix when needed.
  
  @return {string}