gistfile1.js

Y.SquareList = Y.Base.create('squareList', Y.ModelList, [], { /* ... */ });

Y.Game = Y.Base.create('game', Y.Model, [], {
    initializer: function () {
        this._squareList = new Y.SquareList();
    },

    _getSquareList: function () {
        return this._squareList;
    },

    _setSquareList: function (squares) {
        return this._squareList.reset(squares);
    }
}, {
    ATTRS: {
        squareList: {
            getter   : '_getSquareList',
            setter   : '_setSquareList',
            validator: Y.Lang.isArray,
            value    : []
        }
    }
});