if (args.length < 3 || args.length > 4) {
            throw new IllegalArgumentException("USAGE: <style-sheet> <source-file> <dest-file> [dest-dir]");
        }
        File stylesheet = new File(args[0]);
        File source = new File(args[1]);
        File dest = new File(args[2]);
        String destDir = "";
        if (args.length > 3) {
            destDir = args[3];
        }