code: public byte []
  getHexString() throws IOException {
  	String next = _getIdentifier("a hex string");
  	byte [] array = base16.fromString(next);
  	if (array == null)
  		throw exception("invalid hex encoding");
  	return array;
  }
docs: Gets the next token from a tokenizer and decodes it as hex.
  @return The byte array containing the decoded string.
  @throws TextParseException The input was invalid.
  @throws IOException An I/O error occurred.