Setting TextBox text from a ControlTemplate Trigger based on validation error
===

Below is a style for a textbox with a ControlTemplate and Validation. The Style Trigger setting the ToolTip works - so basically I get the reported validation error coming up in the ToolTip. But I also want the validation error to appear in the TextBox named 'ErrorTextBox' -  which does not work.

    <Style x:Key="UiEditorTextBoxStyle"
           TargetType="{x:Type TextBox}">
        <Setter Property="Control.Margin" Value="2,2" />
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type TextBox}">
                    <StackPanel Orientation="Horizontal">
                        <TextBox Text="{Binding Path=Text,
                                                RelativeSource={RelativeSource TemplatedParent},
                                                Mode=TwoWay,
                                                UpdateSourceTrigger=PropertyChanged}"
                                 Background="BlanchedAlmond"
                                 Width="200"/>
                        <TextBox Name="ErrorTextBox"
                                 Background="Azure"
                                 Width="50" />
                                 <!--Text="{Binding ElementName=MyAdorner, 
                                                Path=AdornedElement.(Validation.Errors)[0].ErrorContent}" />-->
                    </StackPanel>
                    <ControlTemplate.Triggers>
                        <Trigger Property="Validation.HasError" Value="true">
                            <Setter TargetName="ErrorTextBox"
                                    Property="Text"
                                    Value="{Binding RelativeSource={RelativeSource Self}, 
                                    Path=AdornedElement.(Validation.Errors)[0].ErrorContent}"/>
                        </Trigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
        <Setter Property="Validation.ErrorTemplate">
            <Setter.Value>
                <ControlTemplate>
                    <StackPanel Orientation="Horizontal">
                        <Border BorderBrush="Red" BorderThickness="1">
                            <AdornedElementPlaceholder />
                        </Border>
                    </StackPanel>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
        <Style.Triggers>
            <Trigger Property="Validation.HasError" Value="true">
                <Setter Property="ToolTip"
                        Value="{Binding RelativeSource={RelativeSource Self}, 
                        Path=(Validation.Errors)[0].ErrorContent}"/>
            </Trigger>
        </Style.Triggers>
    </Style>

Initially I had the Setter for the ErrorTextBox where the Setter for the ToolTip is, but it could then not see the ErrorTextBox ('ErrorTextBox' was not found). Like so:

        <Style.Triggers>
            <Trigger Property="Validation.HasError" Value="true">
                <Setter Property="ToolTip"
                        Value="{Binding RelativeSource={RelativeSource Self}, 
                        Path=(Validation.Errors)[0].ErrorContent}"/>
                <Setter TargetName="ErrorTextBox"
                        Property="Text"
                        Value="{Binding RelativeSource={RelativeSource Self}, 
                        Path=(Validation.Errors)[0].ErrorContent}"/>
            </Trigger>
        </Style.Triggers>

Please, could somebody tell me how to do this?
