title: What's the difference between visibility: hidden and visibility: collapse in flexbox?
body: <p>In the <a href="https://www.w3.org/TR/css-flexbox-1/#visibility-collapse" rel="noreferrer">CSS flexible box layout module</a>, it says:</p>
  
  <blockquote>
    <p>the collapsed flex item is removed from rendering entirely, but leaves behind a "strut"</p>
  </blockquote>
  
  <p>Does that behave just like <code>visibility: hidden</code>? If the answer is yes, then why was <code>visibility: collapse</code> introduced?</p>