title: XAML string length validation
body: <p>I have a Name input field in xaml and I would like to validate the string length that the user is allowed to insert (up to 14 characters).
  I tried to do this:</p>
  
  <pre><code>&lt;PropertyViewDescriptor Name="Name" &gt;
     &lt;PropertyViewDescriptor.Validators&gt;
         &lt;TextValuePattern Pattern=".{1,14}" Message="up to 14 characters"/&gt;
     &lt;/PropertyViewDescriptor.Validators&gt;
  &lt;/PropertyViewDescriptor&gt;
  </code></pre>
  
  <p>But it seems like it checks if the characters are from the set {1,2,3,...,14}.
  What is the correct pattern for length validation?</p>