code: func (e *RecordEncoder) Series(series []RefSeries, b []byte) []byte {
  	buf := encoding.Encbuf{B: b}
  	buf.PutByte(byte(RecordSeries))
  
  	for _, s := range series {
  		buf.PutBE64(s.Ref)
  		buf.PutUvarint(len(s.Labels))
  
  		for _, l := range s.Labels {
  			buf.PutUvarintStr(l.Name)
  			buf.PutUvarintStr(l.Value)
  		}
  	}
  	return buf.Get()
  }
docs: // Series appends the encoded series to b and returns the resulting slice.