title: Check if Unicode Character is Defined in Swift
body: <p>I have a question in regards to if it would be possible to check if a character is defined in iOS unicode for example. </p>
  
  <pre><code>print(Character(UnicodeScalar(9966)))
        //this prints [?]
  print(Character(UnicodeScalar(9955)))
        //this also prints [?]
  </code></pre>
  
  <p>Would there be a way to check if this default character is printed? Or in other words, detect that the character is not defined and will thereby print <code>[?]</code>.</p>