code: func CutOne(b []byte) (data []byte, remain []byte, err error) {
  	l, err := peek(b)
  	if err != nil {
  		return nil, nil, errors.Trace(err)
  	}
  	return b[:l], b[l:], nil
  }
docs: // CutOne cuts the first encoded value from b.
  // It will return the first encoded item and the remains as byte slice.