public List<AltAST> getUnlabeledAltASTs() {
		List<AltAST> alts = new ArrayList<AltAST>();
		for (int i=1; i<=numberOfAlts; i++) {
			GrammarAST altLabel = alt[i].ast.altLabel;
			if ( altLabel==null ) alts.add(alt[i].ast);
		}
		if ( alts.isEmpty() ) return null;
		return alts;
	}
Get {@code #} labels. The keys of the map are the labels applied to outer
alternatives of a lexer rule, and the values are collections of pairs
(alternative number and {@link AltAST}) identifying the alternatives with
this label. Unlabeled alternatives are not included in the result.
tool/src/org/antlr/v4/tool/Rule.java