code: function _setConfig(config, keepExisting) {
          var property;
  
          // optionally clean out the existing properties first
          if (!keepExisting) {
              for (property in _config) {
                  if (_config.hasOwnProperty(property)) {
                      delete _config[property];
                  }
              }
          }
  
          // add in the new properties
          for (property in config) {
              if (config.hasOwnProperty(property)) {
                  _config[property] = config[property];
              }
          }
      }
docs: Set the plugin's config object. This mutates the referenced object, not the
  reference. For automated testing only.
  
  @private
  @param {object} config
  @param {boolean=} keepExisting if true then don't delete previous configs first. default: false