docs: public void addUsageTo(final StringBuilder buf) {
      final ArrayList<String> names = new ArrayList<String>(options.keySet());
      Collections.sort(names);
      int max_length = 0;
      for (final String name : names) {
        final String[] opt = options.get(name);
        final int length = name.length()
          + (opt[0] == null ? 0 : opt[0].length() + 1);
        if (length > max_length) {
          max_length = length;
        }
      }
      for (final String name : names) {
        final String[] opt = options.get(name);
        int length = name.length();
        buf.append("  ").append(name);
        if (opt[0] != null) {
          length += opt[0].length() + 1;
          buf.append('=').append(opt[0]);
        }
        for (int i = length; i <= max_length; i++) {
          buf.append(' ');
        }
        buf.append(opt[1]).append('\n');
      }
    }