docs: private String mkPreview(int line) {
          StringBuilder sb = new StringBuilder();
          int startLine = line - 3;
          int endLine = line + 3;
          List<String> lines = multiSourceReader.getData();
          for (int i = 0; i < lines.size(); i++) {
              if (i >= startLine && i <= endLine) {
                  sb.append(lines.get(i)).append('\n');
              }
          }
          return sb.toString();
      }