title: Get Valdiation error in Tooltip if there is an error, else show explanatory Tooltip (using TextBox Style)
body: <p><strong>Update: Found a Solution, see below!</strong></p>
  
  <p>I'm try to implement the following behavior:</p>
  
  <p>There are several TextBoxes in a UserControl. Each TextBox-ToolTip should show a specific string, which is located in a Resource.resx-file.
  If the Valdiation of this TextBox returns an error, the returned error string will be shown in the ToolTip.
  This should be done using a Style. My current status is, that I can show the specific Validation.Errors AND a <em>default</em> ToolTip, which is the same for every TextBox which uses the Style.</p>
  
  <p>So my Style is :</p>
  
  <pre><code>&lt;Style TargetType="{x:Type TextBox}"&gt; 
      &lt;Setter Property="ToolTip" Value="ExampleToolTip"/&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).CurrentItem.ErrorContent}"/&gt;
          &lt;/Trigger&gt;
      &lt;/Style.Triggers&gt;
  &lt;/Style&gt;
  </code></pre>
  
  <p>With this Style, i get the behavior described above.</p>
  
  <p>Now I want the Style part</p>
  
  <pre><code>&lt;Style TargetType="{x:Type TextBox}"&gt; 
      &lt;Setter Property="ToolTip" Value="ExampleToolTip"/&gt;
      ...
  &lt;/Style&gt;
  </code></pre>
  
  <p>to be TextBox-Specific.</p>
  
  <p>I tried to write an Attatched Property for my TextBoxes, so that I can define a second string, which should be used as the standard ToolTip.</p>
  
  <p>The Attached Property Code ist shown below:</p>
  
  <pre><code>public class TextBox2 : DependencyObject
      {
          public static void SetToolTipStandard(TextBox target, string value)
          {
              target.SetValue(ToolTipStandardProperty, value);
          }
  
          public static string GetToolTipStandard(TextBox target)
          {
              return (string)target.GetValue(ToolTipStandardProperty);
          }
  
          public static DependencyProperty ToolTipStandardProperty = DependencyProperty.RegisterAttached(
              "ToolTipStandard",
              typeof(string),
              typeof(TextBox),
              new PropertyMetadata());
      }
  </code></pre>
  
  <p>Now I want to set a TextBox2.ToolTipStandard property on my TextBoxes in XAML, and the TextBox-Style should take this Property to set the default ToolTip-Text. I tried several combinations of Bindings but with no success. Is there a way to achieve this behavior?</p>