title: ControlTemplate Binding TextBox inside ErrorTemplate
body: <p>My problem is, that I don't get the ToolTip Text thrown by the SetterException of my binding object.</p>
  
  <p>I have a ControlTemplate like this:</p>
  
  <pre><code>&lt;ControlTemplate x:Key="textBoxErrorTemplate" &gt;
      &lt;Grid Margin="-15,5,0,0" ToolTip="{Binding RelativeSource={RelativeSource TemplatedParent},Path=(Validation.Errors)[0].ErrorContent}"&gt;
          &lt;Ellipse StrokeThickness="0" Fill="Red" Width="{TemplateBinding FontSize}" Height="{TemplateBinding FontSize}" /&gt;
          &lt;TextBlock Text="!" FontSize="{TemplateBinding FontSize}" FontWeight="Bold" Foreground="White" HorizontalAlignment="Center"  /&gt;                               
      &lt;/Grid&gt;
  &lt;/ControlTemplate&gt;
  </code></pre>
  
  <p>I also tried </p>
  
  <pre><code>ToolTip="{Binding RelativeSource={RelativeSource Self},Path=(Validation.Errors)[0].ErrorContent}"
  ToolTip="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type TextBox}},Path=(Validation.Errors)[0].ErrorContent}"
  </code></pre>
  
  <p>My TextBox looks like this:</p>
  
  <pre><code>&lt;TextBox Grid.Row="1" Grid.Column="1" Name="tbMin" SourceUpdated="tb_SourceUpdated" Validation.ErrorTemplate="{StaticResource textBoxErrorTemplate}"/&gt;
  </code></pre>
  
  <p>I'm binding the data source in code like this:</p>
  
  <pre><code>Binding bindMinString = new Binding("MinString");
          bindMinString.Source = curStep;
          bindMinString.NotifyOnSourceUpdated = true;
          bindMinString.ValidatesOnExceptions = true;
          bindMinString.UpdateSourceTrigger = UpdateSourceTrigger.PropertyChanged;
          tbMin.SetBinding(TextBox.TextProperty, bindMinString);
  </code></pre>
  
  <p>The template seems to work (I see the ellipse with the "!"), but I don't see my exception message.</p>