title: How to write a value object in XAML using markup extension?
body: <p>I want to replace </p>
  
  <pre><code>&lt;Button Text="Foo" Command="{Binding Foo}"&gt;
      &lt;Button.CommandParameter&gt;
          &lt;System:Boolean&gt;True&lt;/System:Boolean&gt;
      &lt;/Button.CommandParameter&gt;
  &lt;/Button&gt;
  </code></pre>
  
  <p>with something like </p>
  
  <pre><code>&lt;Button ... CommandParameter="{???}"/&gt;
  </code></pre>