Filtering the WPF DataGrid automatically via the header (inline filtering)

<ResourceDictionary
   xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
   xmlns:local="clr-namespace:Labs.Filtering"
   xmlns:my="http://schemas.microsoft.com/wpf/2008/toolkit">

    <local:HeaderFilterConverter x:Key="headerConverter"/>

    <Style TargetType="{x:Type my:DataGridColumnHeader}">
        <Setter Property="VerticalContentAlignment" Value="Center"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type my:DataGridColumnHeader}">
                    <ControlTemplate.Resources>
                        <Storyboard x:Key="ShowFilterControl">
                            <ObjectAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetName="filterTextBox" Storyboard.TargetProperty="(UIElement.Visibility)">
                                <DiscreteObjectKeyFrame KeyTime="00:00:00" Value="{x:Static Visibility.Visible}"/>
                                <DiscreteObjectKeyFrame KeyTime="00:00:00.5000000" Value="{x:Static Visibility.Visible}"/>
                            </ObjectAnimationUsingKeyFrames>
                            <ColorAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetName="filterTextBox" Storyboard.TargetProperty="(Panel.Background).(SolidColorBrush.Color)">
                                <SplineColorKeyFrame KeyTime="00:00:00" Value="Transparent"/>
                                <SplineColorKeyFrame KeyTime="00:00:00.5000000" Value="White"/>
                            </ColorAnimationUsingKeyFrames>
                        </Storyboard>
                        <Storyboard x:Key="HideFilterControl">
                            <ObjectAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetName="filterTextBox" Storyboard.TargetProperty="(UIElement.Visibility)">
                                <DiscreteObjectKeyFrame KeyTime="00:00:00.4000000" Value="{x:Static Visibility.Collapsed}"/>
                            </ObjectAnimationUsingKeyFrames>
                            <ColorAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetName="filterTextBox" Storyboard.TargetProperty="(UIElement.OpacityMask).(SolidColorBrush.Color)">
                                <SplineColorKeyFrame KeyTime="00:00:00" Value="Black"/>
                                <SplineColorKeyFrame KeyTime="00:00:00.4000000" Value="#00000000"/>
                            </ColorAnimationUsingKeyFrames>
                        </Storyboard>
                    </ControlTemplate.Resources>
                        <my:DataGridHeaderBorder x:Name="dataGridHeaderBorder" Margin="0" VerticalAlignment="Top" Height="31" IsClickable="{TemplateBinding CanUserSort}" IsHovered="{TemplateBinding IsMouseOver}" IsPressed="{TemplateBinding IsPressed}" SeparatorBrush="{TemplateBinding SeparatorBrush}" SeparatorVisibility="{TemplateBinding SeparatorVisibility}" SortDirection="{TemplateBinding SortDirection}" Background="{TemplateBinding Background}" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Padding="{TemplateBinding Padding}" Grid.ColumnSpan="1">
                            <Grid x:Name="grid" Width="Auto" Height="Auto" RenderTransformOrigin="0.5,0.5">
                                <Grid.RenderTransform>
                                    <TransformGroup>
                                        <ScaleTransform/>
                                        <SkewTransform/>
                                        <RotateTransform/>
                                        <TranslateTransform/>
                                    </TransformGroup>
                                </Grid.RenderTransform>
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition Width="*"/>
                                </Grid.ColumnDefinitions>
                            <ContentPresenter x:Name="contentPresenter"
                                    HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}" 
                                    VerticalAlignment="{TemplateBinding VerticalContentAlignment}" 
                                    SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" 
                                    ContentStringFormat="{TemplateBinding ContentStringFormat}" 
                                    ContentTemplate="{TemplateBinding ContentTemplate}">
                                <ContentPresenter.Content>
                                        <MultiBinding Converter="{StaticResource headerConverter}">
                                            <MultiBinding.Bindings>
                                                <Binding ElementName="filterTextBox" Path="Text" />
                                                <Binding RelativeSource="{RelativeSource TemplatedParent}" Path="Content" />
                                            </MultiBinding.Bindings>
                                        </MultiBinding>
                                </ContentPresenter.Content>
                            </ContentPresenter>
                            <TextBox x:Name="filterTextBox" HorizontalAlignment="Right" MinWidth="25" Height="Auto" OpacityMask="Black" Visibility="Collapsed" Text="" TextWrapping="Wrap" Grid.Column="0" Grid.ColumnSpan="1"/>
                            </Grid>
                      </my:DataGridHeaderBorder>                      
                    <ControlTemplate.Triggers>
                        <Trigger Property="IsMouseOver" Value="True">
                            <Trigger.EnterActions>
                                <BeginStoryboard x:Name="ShowFilterControl_BeginStoryboard" Storyboard="{StaticResource ShowFilterControl}"/>
                                <StopStoryboard BeginStoryboardName="HideFilterControl_BeginShowFilterControl"/>
                            </Trigger.EnterActions>
                            <Trigger.ExitActions>
                                <BeginStoryboard x:Name="HideFilterControl_BeginShowFilterControl" Storyboard="{StaticResource HideFilterControl}"/>
                                <StopStoryboard BeginStoryboardName="ShowFilterControl_BeginStoryboard"/>
                            </Trigger.ExitActions>
                        </Trigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</ResourceDictionary>