code: function error(msg) {
    if (PDFJS.verbosity >= PDFJS.VERBOSITY_LEVELS.errors) {
      console.log('Error: ' + msg);
      console.log(backtrace());
    }
    UnsupportedManager.notify(UNSUPPORTED_FEATURES.unknown);
    throw new Error(msg);
  }
docs: Fatal errors that should trigger the fallback UI and halt execution by throwing an exception.