title: Tilde in front of .box-shadow value
body: <p>I was looking at bootsrap mixins.less and noticed a tilde in front of box-shadow value. What purpose does it serve? If my website supports IE9 and higher should I be using it?</p>
  
  <pre><code>.box-shadow(~"inset 0 1px 1px rgba(0,0,0,.075), 0 0 8px @{color-rgba}");
  </code></pre>