public Set<String> getTokenRefs() {
        Set<String> refs = new HashSet<String>();
		for (int i=1; i<=numberOfAlts; i++) {
			refs.addAll(alt[i].tokenRefs.keySet());
		}
		return refs;
    }
Lexer actions are numbered across rules 0..n-1
tool/src/org/antlr/v4/tool/Rule.java