title: Sass % operator
body: <p>One of the developers where I work recently left and upon going through his sass code, I found this:</p>
  
  <pre><code>%centerAll {
    display: block;
    position: relative;
    top: 50%;
    left: 50%;
    -webkit-transform: translate(-50%, -50%);
    -ms-transform: translate(-50%, -50%);
    transform: translate(-50%, -50%);
  }
  </code></pre>
  
  <p>I'd say I'm pretty experienced with sass but I've never see anything in Sass that uses the modulo operator like that. To make matters stranger, this "mixin" is included through the code as:</p>
  
  <p><code>@extend %centerAll</code></p>
  
  <p>and as far as I know, <code>@extend</code> is used for extending the properties of the class, via inheritance.</p>
  
  <p>Has anyone ever seen this before? </p>