Swift: Understanding // MARK
<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>