title: Swift: Understanding // MARK
body: <p>What is the purpose of writing comments in Swift as:</p>
  
  <pre class="lang-c prettyprint-override"><code>// MARK: This is a comment
  </code></pre>
  
  <p>When you can also do:</p>
  
  <pre class="lang-c prettyprint-override"><code>// This is a comment
  </code></pre>
  
  <p>What does the <code>// MARK</code> achieve?</p>