title: DoubleAnimation exception when animating grid width with DataTrigger
body: <p>I'm trying to animate a grid's width upon a toggle button being checked. I've used a data trigger in the Grid's style element to do this, however, whenever it's triggered I get an error, stating: </p>
  
  <blockquote>
    <p>Cannot animate the 'Width' property on a
    'System.Windows.Controls.Grid' using a
    'System.Windows.Media.Animation.DoubleAnimation'</p>
  </blockquote>
  
  <p>I'm pretty sure it is possible to animate the grid in the way I'm attempting, as I've gotten it to work using a click event. Does anyone see where I'm going wrong here?</p>
  
  <pre><code>&lt;Grid Margin="0" HorizontalAlignment="Left"
            TextOptions.TextFormattingMode="Display" x:Name="MainGrid" &gt;
  
          &lt;Grid.Resources&gt;
              &lt;Style TargetType="Grid"&gt;
                  &lt;Style.Setters&gt;
                      &lt;Setter Property="Width" Value="300"/&gt;
                  &lt;/Style.Setters&gt;
                  &lt;Style.Triggers&gt;
                      &lt;DataTrigger Binding="{Binding Path=IsChecked, ElementName=CollapseIcon}" Value="True"&gt;
  
                          &lt;DataTrigger.EnterActions&gt;
                              &lt;BeginStoryboard &gt;
                                  &lt;Storyboard &gt;
                                      &lt;DoubleAnimation Duration="0:0:0.200" Storyboard.TargetProperty="Width" To="16" /&gt;
                                  &lt;/Storyboard&gt;
                              &lt;/BeginStoryboard&gt;
                          &lt;/DataTrigger.EnterActions&gt;
                      &lt;/DataTrigger&gt;
  
                  &lt;/Style.Triggers&gt;
              &lt;/Style&gt;
  
          &lt;/Grid.Resources&gt;
  </code></pre>