title: What is the reason to have (square) brackets in an element's class name?
body: <p>I was really surprised by this statement <code>class="[ col-xs-12 col-sm-offset-1 col-sm-5 ]"</code> in a bootstrap 3 template and I am not sure what is the difference between </p>
  
  <pre><code>class="[ col-xs-12 col-sm-offset-1 col-sm-5 ]"   
  </code></pre>
  
  <p>and</p>
  
  <pre><code>class="col-xs-12 col-sm-offset-1 col-sm-5"
  </code></pre>
  
  <p>Can you please give me more details about the meaning of this brackets and some cases when they are used?</p>