code: func Split(b []byte) (k Kind, content, rest []byte, err error) {
  	k, ts, cs, err := readKind(b)
  	if err != nil {
  		return 0, nil, b, err
  	}
  	return k, b[ts : ts+cs], b[ts+cs:], nil
  }
docs: // Split returns the content of first RLP value and any
  // bytes after the value as subslices of b.