title: Xaml: Using a child control trigger to change a parent control property
body: <p>I'm attempting to modify a property of a parent control via a trigger on a child control. Specifically, I'm attempting to modify the opacity of a Border's DropShaddowEffect via the OnKeyboardFocus trigger of the Border's child TextBox. </p>
  
  <p>However, the setter's TargetName gives an error that the name is not recognized.</p>
  
  <p>Here is the XAML:</p>
  
  <pre><code>&lt;Border x:Name="HeaderTextBoxBorder"&gt;
      &lt;Border.Effect&gt;
          &lt;DropShadowEffect Opacity="20"/&gt;                                    
      &lt;/Border.Effect&gt;
      &lt;TextBox x:Name="HeaderTextBox"&gt;
          &lt;TextBox.Style&gt;
              &lt;Style
                  TargetType="{x:Type TextBox}"&gt;
                  &lt;!-- Attmpting to change opacity on focus --&gt;
                  &lt;Style.Triggers&gt;
                      &lt;Trigger
                          Property="IsKeyboardFocused"
                          Value="True"&gt;
                              &lt;Setter
                                  &lt;!-- The error occurs here --&gt;
                                  TargetName="HeaderTextBoxBorder"
                                  Property="Effect"&gt;
                                  &lt;Setter.Value&gt;
                                      &lt;DropShadowEffect Opacity="100"/&gt;
                                  &lt;/Setter.Value&gt;
                              &lt;/Setter&gt;
                      &lt;/Trigger&gt;
                  &lt;/Style.Triggers&gt;   
              &lt;/Style&gt;
          &lt;/TextBox.Style&gt;
      &lt;/TextBox&gt;
  &lt;/Border&gt;
  </code></pre>
  
  <p>Looking at the XAML, is there anything that pops out as incorrect?</p>
  
  <p>Thank you for your time.</p>