title: TextBox Validation ToolTip Not Appearing
body: <p>I have the following Style for a TextBox:</p>
  
  <pre class="lang-xml prettyprint-override"><code>&lt;Style x:Key="RenamingTextBox" TargetType="{x:Type TextBox}"&gt;
          &lt;Style.Setters&gt;
              &lt;Setter Property="Template"&gt;
                  &lt;Setter.Value&gt;
                      &lt;ControlTemplate TargetType="{x:Type TextBox}"&gt;
                          &lt;Grid&gt;
                              &lt;TextBlock x:Name="block" Visibility="Visible" Text="{TemplateBinding Text}" Margin="0"/&gt;
                              &lt;TextBox x:Name="box" Visibility="Collapsed" 
                                       Text="{Binding Text, RelativeSource={RelativeSource TemplatedParent}, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" 
                                       Margin="1.25"/&gt;
                          &lt;/Grid&gt;
                          &lt;ControlTemplate.Triggers&gt;
                              &lt;DataTrigger Binding="{Binding IsRenaming}" Value="true"&gt;
                                  &lt;DataTrigger.Setters&gt;
                                      &lt;Setter TargetName="block" Property="TextBox.Visibility" Value="Collapsed" /&gt;
                                      &lt;Setter TargetName="box" Property="TextBox.Visibility" Value="Visible" /&gt;
                                      &lt;Setter TargetName="box" Property="FocusManager.FocusedElement" Value="{Binding ElementName=box}" /&gt;
                                      &lt;Setter TargetName="box" Property="behaviors:TextBoxBehavior.SelectAll" Value="True"/&gt;
                                  &lt;/DataTrigger.Setters&gt;
                              &lt;/DataTrigger&gt;
                          &lt;/ControlTemplate.Triggers&gt;
                      &lt;/ControlTemplate&gt;
                  &lt;/Setter.Value&gt;
              &lt;/Setter&gt;
          &lt;/Style.Setters&gt;
      &lt;/Style&gt;
  </code></pre>
  
  <p>and also:</p>
  
  <pre class="lang-xml prettyprint-override"><code>&lt;Style TargetType="{x:Type TextBox}"&gt;
      &lt;Setter Property="Margin" Value="5" /&gt;
      &lt;Setter Property="VerticalAlignment" Value="Center" /&gt;
      &lt;Setter Property="BorderBrush" Value="LightGray" /&gt;
      &lt;Style.Triggers&gt;
          &lt;Trigger Property="Validation.HasError" Value="True"&gt;
              &lt;Setter Property="ToolTip" 
                      Value="{Binding RelativeSource={RelativeSource Self},
                      Path=(Validation.Errors)[0].ErrorContent}"/&gt;
          &lt;/Trigger&gt;
      &lt;/Style.Triggers&gt;
  &lt;/Style&gt;
  </code></pre>
  
  <p>The renaming textbox works great, it changes back and forth from TextBox to TextBlock with no problem. It even gets the nice red border when there is an error in my Name. The problem is that the ToolTip doesn't show up when I hover over the textbox with an error. All my other TextBoxes in the project work fine. Any ideas?</p>