private static Result invalid(int start, int stop) { // start..stop is inclusive
		return new Result(
			Result.Type.INVALID,
			0,
			IntervalSet.EMPTY_SET,
			start,
			stop - start + 1);
	}
Parses a single escape sequence starting at {@code startOff}.

Returns a type of INVALID if no valid escape sequence was found, a Result otherwise.
tool/src/org/antlr/v4/misc/EscapeSequenceParsing.java