code: function defaultEngine (engine) {
      // set engine
      if (defined(engine)) {
          getGlobal().defaultEngine = engine
          // return class when setting
          return ImmutableCoreModel
      }
      // return engine
      return getGlobal().defaultEngine
  }
docs: @function defaultEngine
  
  get/set global default database engine used when creating tables
  
  @param {string|undefined} engine
  
  @returns {ImmutableCoreModel|string}