public static String getIntervalSetEscapedString(IntervalSet intervalSet) {
		StringBuilder buf = new StringBuilder();
		Iterator<Interval> iter = intervalSet.getIntervals().iterator();
		while (iter.hasNext()) {
			Interval interval = iter.next();
			buf.append(getRangeEscapedString(interval.a, interval.b));
			if (iter.hasNext()) {
				buf.append(" | ");
			}
		}
		return buf.toString();
	}
Given char x or \\t or \\u1234 return the char value;
 Unnecessary escapes like '\{' yield -1.
tool/src/org/antlr/v4/misc/CharSupport.java