title: Check element type inside a class selector
body: <p>In Sass, we all use to do things like this:</p>
  
  <pre><code>button {
    @extend %button;
  
    &amp;.previous,
    &amp;.next {
      background: blue;
    }
  }
  </code></pre>
  
  <p>Today, I need the exact opposite: check the element type inside a class selector. Here's my first attempt, which I expected to work:</p>
  
  <pre><code>.previous,
  .next {
    @extend %button;
  
    &amp;span {
      opacity: .3;
    }
  }
  </code></pre>
  
  <p>Unfortunately, this outputs selectors like <code>.previousspan</code> and <code>.nextspan</code>. I tried to use <code>span&amp;</code>, or interpolation as I highly suppose it could solve my problem, but I'm stuck.</p>
  
  <p>Any idea?  </p>
  
  <blockquote>
    <p>Note: I could obviously put this <code>span</code> selector outside (and that's what I've done to get it to work), but this is not the point of my question. I'm really searching for the <em>right</em> way to do it, thanks.</p>
  </blockquote>