title: Allow Backspace with character set
body: <p>I am having trouble deleting in my text field. So I have a text field for a person name only allowing letters. But when I hit the delete or backspace it doesn't seem to work. This is what my code looks like.</p>
  
  <pre><code> func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -&gt; Bool {
      let set = CharacterSet.letter
      return (string.rangeOfCharacter(from: set) != nil)
  }
  </code></pre>
  
  <p>I am not sure why the backspace/delete is not working. </p>