code: function showError(cfg = {}) {
      if (_.isBoolean(cfg) && !cfg && errorDoc) { // hide error
          navigationDocument.removeDocument(errorDoc);
          return;
      }
      if (_.isString(cfg)) {
          cfg = {
              data: {
                  message: cfg
              }
          };
      }
      // use default error template if not passed as a configuration
      _.defaultsDeep(cfg, {
          template: defaults.templates.error
      });
  
      console.log('showing error... options:', cfg);
  
      // cache the doc for later use
      errorDoc = show(cfg);
  
      return errorDoc;
  }
docs: Shows the error page using the existing error template.
  Also applies any default handlers and caches the document for later use.
  
  @inner
  @alias module:navigation.showError
  
  @param  {Object|Function|Boolean} cfg    The configuration options or the template function or boolean to hide the error
  @return {Document}                       The created error document.