title: RelativeSource Sibling
body: <p>Below tabitem3 is working fine.<br>
  I would like to get away from naming the controls and pass the properties by RelativeSource.   </p>
  
  <p>The code that is failing is </p>
  
  <pre><code>Binding RelativeSource="{RelativeSource AncestorType={x:Type Expander}}" Path="IsExpanded"
  </code></pre>
  
  <p>The error in the converter is dependency object not set</p>
  
  <p>The Expander is a sibling not an ancestor.<br>
  How can I find that sibling (without an x:Name)?</p>
  
  <pre><code>&lt;TabItem x:Name="tabitem3" IsSelected="False"&gt;
      &lt;TabItem.Header&gt;
          &lt;Expander x:Name="tabexp3" Header="Three" IsHitTestVisible="True"
                    Expanded="expcolp" Collapsed="expcolp" IsExpanded="False"/&gt;
      &lt;/TabItem.Header&gt;
      &lt;TextBlock Text="Content Three TabItem" Background="LightBlue" &gt;
          &lt;TextBlock.Visibility&gt;
              &lt;MultiBinding Converter="{StaticResource bvc2}" Mode="OneWay"&gt;
                   &lt;Binding ElementName="tabexp3"  Path="IsExpanded"/&gt;
                   &lt;Binding ElementName="tabitem3" Path="IsSelected" /&gt;
              &lt;/MultiBinding&gt;
          &lt;/TextBlock.Visibility&gt;
      &lt;/TextBlock&gt;
  &lt;/TabItem&gt;
  &lt;TabItem IsSelected="False"&gt;
      &lt;TabItem.Header&gt;
          &lt;Expander Header="Four" IsHitTestVisible="True"
                    Expanded="expcolp" Collapsed="expcolp" IsExpanded="False"/&gt;
      &lt;/TabItem.Header&gt;
      &lt;TextBlock Text="Content Four TabItem" Background="LightBlue" &gt;
          &lt;TextBlock.Visibility&gt;
              &lt;MultiBinding Converter="{StaticResource bvc2}" Mode="OneWay"&gt;
                   &lt;Binding RelativeSource="{RelativeSource AncestorType={x:Type Expander}}" Path="IsExpanded"/&gt;
                   &lt;Binding RelativeSource="{RelativeSource AncestorType={x:Type TabItem}}"  Path="IsSelected"/&gt;                          
              &lt;/MultiBinding&gt;
          &lt;/TextBlock.Visibility&gt;
      &lt;/TextBlock&gt;
  &lt;/TabItem&gt;
  </code></pre>