@Override
	protected Tree extension(Tree t, String s, int begin, int end) throws ParseException {
		if (begin >= end) {
			return null;
		}
		if (t.node.equals("StringLiteral")) {
			return string(t, s, begin, end);
		} else if (t.node.equals("IntegerLiteral")) {
			return number(t, s, begin, end);
		} else if (t.node.equals("CharacterLiteral")) {
			return string(t, s, begin, end);
		} else if (t.node.equals("FloatingPointLiteral")) {
			return number(t, s, begin, end);
		} else {
			return null; // Not an extension of this parser.
		}
	}