title: Why each font in customFonts tag is a mutable array?
body: <p>For a long time I was curios about the XML behind the any storyboard file. And I try to understand each part of it.</p>
  
  <p>This time I would like to know about this:</p>
  
  <pre><code>&lt;customFonts key="customFonts"&gt;
      &lt;mutableArray key="FontName-Bold.otf"&gt;
          &lt;string&gt;FontName-Bold&lt;/string&gt;
      &lt;/mutableArray&gt;
      &lt;mutableArray key="FontName.otf"&gt;
          &lt;string&gt;FontName&lt;/string&gt;
          &lt;string&gt;FontName&lt;/string&gt;
          &lt;string&gt;FontName&lt;/string&gt;
          &lt;string&gt;FontName&lt;/string&gt;
          &lt;string&gt;FontName&lt;/string&gt;
          &lt;string&gt;FontName&lt;/string&gt;
          &lt;string&gt;FontName&lt;/string&gt;
      &lt;/mutableArray&gt;
  &lt;/customFonts&gt;
  </code></pre>
  
  <p>Why it is a mutable array? Why there are a lot of occurrences for the second font, but only one for the first? </p>