Storyboard not executing from ControlTemplate DataTrigger - wpf

Question

I have a ToggleButton which I click to popup a FlowDocumentReader as an Adorner. This FlowDocument is part of a ControlTemplate with a DataTrigger to show/hide the element.
Using the following Trigger everything works fine. I use a DataTrigger and some Setters, my element displays correctly with Height and Width I provide when I check my ToggleButton:
<ControlTemplate.Triggers>
<DataTrigger Binding="{Binding ElementName=adorner, Path=AdornedElement.IsChecked}" Value="True" >
<Setter TargetName="mainBorder" Property="Height" Value="437"></Setter>
<Setter TargetName="mainBorder" Property="Width" Value="537"></Setter>
</DataTrigger>
</ControlTemplate.Triggers>
I want to have some animation that occurs as my element appears, so I tried to used a Storyboard. This doesn't work, nothing seems to happen:
<ControlTemplate.Triggers>
<DataTrigger Binding="{Binding ElementName=adorner, Path=AdornedElement.IsChecked}" Value="True" >
<DataTrigger.EnterActions>
<BeginStoryboard>
<Storyboard Storyboard.TargetName="mainBorder">
<DoubleAnimation Duration="0:0:0.2" Storyboard.TargetProperty="Width" To="537" />
<DoubleAnimationUsingKeyFrames BeginTime="0:0:0.2" Duration="0:0:0.3" Storyboard.TargetProperty="Height">
<LinearDoubleKeyFrame Value="417" KeyTime="0:0:0.2" />
<LinearDoubleKeyFrame Value="437" KeyTime="0:0:0.24" />
<LinearDoubleKeyFrame Value="417" KeyTime="0:0:0.3" />
</DoubleAnimationUsingKeyFrames>
</Storyboard>
</BeginStoryboard>
</DataTrigger.EnterActions>
<DataTrigger.ExitActions>
<BeginStoryboard>
<Storyboard Storyboard.TargetName="mainBorder">
<DoubleAnimationUsingKeyFrames Duration="0:0:0.2" Storyboard.TargetProperty="Width">
<LinearDoubleKeyFrame Value="0" KeyTime="0:0:0.2" />
</DoubleAnimationUsingKeyFrames>
<DoubleAnimationUsingKeyFrames BeginTime="0:0:0.2" Duration="0:0:0.2" Storyboard.TargetProperty="Height">
<LinearDoubleKeyFrame Value="0" KeyTime="0:0:0.2" />
</DoubleAnimationUsingKeyFrames>
</Storyboard>
</BeginStoryboard>
</DataTrigger.ExitActions>
</DataTrigger>
</ControlTemplate.Triggers>
Is the Storyboard context completely different than the Setter? Why does it work in one place, but not the other?
Oddly enough, when I make this change, it causes a binding error to display in the Output Window. I haven't touched the actual binding for the DataTrigger, just the contents:
System.Windows.Data Error: 4 : Cannot find source for binding with
reference 'ElementName=adorner'.
BindingExpression:Path=AdornedElement.IsChecked; DataItem=null; target
element is 'Control' (Name=''); target property is 'NoTarget' (type
'Object')
Here is a general idea of the rest of the template:
<ControlTemplate x:Key="LocalHelpWindow">
<Grid>
<Grid.RowDefinitions>
...
</Grid.RowDefinitions>
<help:AdornedPlaceholder x:Name="adorner" Grid.Row="0"/>
<Border Grid.Row="1" x:Name="mainBorder">
...
</Border>
</Grid>
<ControlTemplate.Triggers>
<DataTrigger Binding="{Binding ElementName=adorner, Path=AdornedElement.IsChecked}" Value="True" >
...
</DataTrigger>
</ControlTemplate.Triggers>
</ControlTemplate>

Answer 1

I think in your case you should use Trigger instead of DataTrigger. DataTrigger is using to bind to some data in DataContext of element in which DataTemplate was applied.
I suggest you try to use Trigger in that way:
<Trigger SourceName="adorner" Property="AdornedElement.IsChecked" Value="True">
...
</Trigger>