title: InputScope dependency property, XAML designer problems + errors
body: <p>I have a control that consists of a button and a textbox.</p>
  
  <p>I wanted to set the input scope of the textbox, so I introduced a new dependency property:</p>
  
  <pre><code>public InputScope InputScope
  {
      get { return (InputScope)GetValue(InputScopeProperty); }
      set { SetValue(InputScopeProperty, value); } // Notify prop change
  }
  
  public static readonly DependencyProperty InputScopeProperty =
              DependencyProperty.Register(nameof(InputScope), typeof(InputScope), typeof(SearchControl), new PropertyMetadata(DependencyProperty.UnsetValue));
  </code></pre>
  
  <p>In XAML:</p>
  
  <pre><code>&lt;controls:SearchControl InputScope="Number" /&gt; &lt;!-- etc... --&gt;
  </code></pre>
  
  <p>(Obviously assigning it to the InputScope property of the textbox in the style of this custom control.)</p>
  
  <p><strong>My problem:</strong> While this works, the numeric keyboard gets shown when focused, but I have blue underline in the XAML, and also an error message: The TypeConverter for "InputScope" does not support converting from a string.</p>
  
  <p>Is there a way to fix it without a dirty hack?</p>