public void
unget() {
	if (ungottenToken)
		throw new IllegalStateException
				("Cannot unget multiple tokens");
	if (current.type == EOL)
		line--;
	ungottenToken = true;
}
Returns a token to the stream, so that it will be returned by the next call
to get().
@throws IllegalStateException There are already ungotten tokens.
src/main/java/core/org/xbill/DNS/Tokenizer.java