ZURB Foundation XY-Grid grid-y-对小的视口高度的响应能力？

Question

我有这个标记，包括Foundation 6类：

<div class="grid-container">

<div class="grid-x grid-padding-x">
  <div class="large-12 cell">
    <h1>Welcome to my Testingsite!</h1>
  </div>
</div>

<div class = "grid-x grid-margin-x">
  <div class = "cell large-4 medium-6 small-12">
    <img src = "Ressources/DNAPictures/1.png">
  </div>
  <div class = "cell large-4 medium-6 small-12">
    <img src = "Ressources/DNAPictures/2.gif">
  </div>
  <div class = "cell large-4 medium-6 small-12">
    <img src = "Ressources/DNAPictures/3.gif">
  </div>

<div class = "grid-y grid-margin-y">
 <div class = "cell large-4 medium-6 small-12 shrink">
   <img src = "Ressources/DNAPictures/4.png">
 </div>
 <div class = "cell large-4 medium-6 small-12 shrink">
   <img src = "Ressources/DNAPictures/5.png">
 </div>
 <div class = "cell large-4 medium-6 small-12 shrink">
   <img src = "Ressources/DNAPictures/6.jpg">
 </div>

 </div>

现在，由于grid-x元素在视口宽度变小时垂直包裹，所以我希望grid-y元素在视口高度变小时水平包裹。 但这并没有发生，我也没有在官方教程中找到任何有用的信息，互联网上也没有其他地方。 grid-y元素的预期“包装行为”是什么？