title: Setting space between some items in stack view
body: <p>In Interface Builder, I use a horizontal UIStackView and want to place the items as this :</p>
  
  <pre><code>   xx   xx   xx
  </code></pre>
  
  <p>every x symbolize an item. Item1 and item2 should be stuck one to the other, but item2 and item3 should be spaced and so on. That means I do not want constant spacing between all the items.</p>
  
  <p>How can I do so ?<br>
  (maybe an equivalent of flexible space of toolbars) </p>
  
  <p>Thanks !</p>