How to use IsEnabledChanged event on element inside style?

Question

I have an element specified inside a style. I need the codebehind to know when IsEnabled changes on one of the elements (the Border in this simplified example), so initially I just set the event like normal:

<UserControl.Resources>
    <Style x:Key="TypedValueHelper" TargetType="ContentControl">
        <Style.Triggers>
            <DataTrigger Binding="{Binding Type, RelativeSource={RelativeSource FindAncestor, AncestorType=UserControl}}"
                         Value="Markdown">
                <Setter Property="ContentTemplate">
                    <Setter.Value>
                        <DataTemplate>
                            <Border x:Name="BorderThing"
                                    IsEnabledChanged="BorderThing_IsEnabledChanged"/>
                        </DataTemplate>
                    </Setter.Value>
                </Setter>
            </DataTrigger>
        </Style.Triggers>
    </Style>
</UserControl.Resources>

Then Visual Studio complained at me and I remembered that you can't set events directly on an element in a style, so I fixed it:

<UserControl.Resources>
    <Style x:Key="BorderThing" TargetType="Border">
        <EventSetter Event="IsEnabledChanged" Handler="BorderThing_IsEnabledChanged"/>
    </Style>
    
    <Style x:Key="TypedValueHelper" TargetType="ContentControl">
        <Style.Triggers>
            <DataTrigger Binding="{Binding Type, RelativeSource={RelativeSource FindAncestor, AncestorType=UserControl}}"
                         Value="Markdown">
                <Setter Property="ContentTemplate">
                    <Setter.Value>
                        <DataTemplate>
                            <Border x:Name="BorderThing"/>
                        </DataTemplate>
                    </Setter.Value>
                </Setter>
            </DataTrigger>
        </Style.Triggers>
    </Style>
</UserControl.Resources>

But now it's telling me The event 'IsEnabledChanged' is not a RoutedEvent ☹

How do I get my event?