docs: function Collection(options) {
    Base.call(this, options);
    this.define('lists', {});
    this.define('_items', {});
    this.define('Item', this.options.Item || require('./item'));
    this.define('List', this.options.List || require('./list'));
    mixins(this);
  
    /**
     * Get an object representing the current items on the instance.
     *
     * ```js
     * var items = this.items;
     * ```
     *
     * @return {Object} Object of items
     */
  
    Object.defineProperty(this, 'items', {
      enumerable: false,
      configurable: true,
      get: function () {
        return this._items;
      },
      set: function (items) {
        lazy.forIn(items, function (item, key) {
          delete this._items[key];
          delete this[key];
          this.set(key, item);
        }, this);
      }
    });
  }