title: WPF Binding with RelativeSource of Window Requires "DataContext" in Path?
body: <p>The following code works, but I'm curious as to why I need the Path to be prefixed with "DataContext"?  In most other cases, the path used is relative to DataContext.  Is it because I am using a RelativeSource?  Because the source is at the root level (Window)?</p>
  
  <pre><code>    &lt;Style TargetType="TextBox"&gt;
          &lt;Setter 
             Property="IsReadOnly"
             Value="{Binding RelativeSource={RelativeSource FindAncestor, 
             AncestorType={x:Type Window}}, Path=DataContext.IsReadOnly}"/&gt;
      &lt;/Style&gt;        
  </code></pre>