public IntervalSet nextTokens(ATNState s, RuleContext ctx) {
		LL1Analyzer anal = new LL1Analyzer(this);
		IntervalSet next = anal.LOOK(s, ctx);
		return next;
	}
Compute the set of valid tokens that can occur starting in state {@code s}.
 If {@code ctx} is null, the set of tokens will not include what can follow
 the rule surrounding {@code s}. In other words, the set will be
 restricted to tokens reachable staying within {@code s}'s rule.
runtime/Java/src/org/antlr/v4/runtime/atn/ATN.java