code: function(settings) {
        settings = settings || {};
  
        // if we got a string, instead of a settings object, use that string as the content
        if (typeof settings === 'string') {
          settings = { content: settings };
        }
  
        // add new settings to our settings object
        [
          'content',
          'content-url',
          'assets',
          'service-worker-url',
          'cache-version',
        ].forEach(function(settingName) {
          if (settings[settingName] !== undefined) {
            _settings[settingName] = settings[settingName];
          }
        });
  
        // Add scope setting
        if (settings['scope'] !== undefined) {
          _settings['registration-options']['scope'] = settings['scope'];
        }
      }
docs: Adds settings to configure how UpUp behaves.
  Call this before running start, or just pass the settings object when calling the start method.
  
  Receives a mandatory settings object. See Settings section of docs for details.
  
  #### Examples:
  ````javascript
  // Set up offline mode with a basic message
  UpUp.addSettings({ content: 'Cannot reach site. Please check your internet connection.' });
  UpUp.start();
  
  // The same thing can be achieved like this
  UpUp.start({ content: 'Cannot reach site. Please check your internet connection.' });
  ````
  
  @param {Object} [settings] - Settings for offline mode
  @method addSettings
  @see [Settings](#settings)