How to Clear Triggered Control Template - wpf

Question

I am trying to achieve the "hint text" functionality for a TextBox in WPF. I can set the default text fine, but the problem comes when I want the control to return its appearance to a normal TextBox. Here is the trigger I have so far:
Trigger A
<Trigger Property="Text" Value="{x:Static sys:String.Empty}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="TextBox">
<TextBox>
<TextBox.Background>
<VisualBrush AlignmentX="Left" AlignmentY="Center" Stretch="UniformToFill">
<VisualBrush.Visual>
<Label Content="{TemplateBinding TextBox.Tag}" Background="White"/>
</VisualBrush.Visual>
</VisualBrush>
</TextBox.Background>
</TextBox>
</ControlTemplate>
</Setter.Value>
</Setter>
</Trigger>
This sets the Background to a VisualBrush when the Text property is empty. What I need to do is clear this ControlTemplate when the user selects the TextBox to input text.
Here is what I tried:
Trigger B
<Trigger Property="IsKeyboardFocused" Value="True">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="TextBox">
<TextBox/>
</ControlTemplate>
</Setter.Value>
</Setter>
</Trigger>
These two don't work together. I tested each by changing the Background colors. If I comment out either one, they will each work. If both are uncommented, Trigger A works and B is never seen. How can I remove/overwrite Trigger A?
I know that the functionality of these templates is supposed to clear when the trigger condition is no longer met, but for example, Trigger A's setting will not go away when I enter text into the TextBox like it should. Like the Text property is still String.Empty or something.
So what am I missing?
EDIT:
Here is the whole style (there's not much more to it):
<UserControl.Resources>
<Style TargetType="TextBox" x:Key="FormsTextBox">
<Setter Property="Width" Value="45"/>
<Setter Property="Margin" Value="3 2 3 2"/>
<Style.Triggers>
<Trigger Property="Text" Value="{x:Static sys:String.Empty}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="TextBox">
<TextBox>
<TextBox.Background>
<VisualBrush AlignmentX="Left" AlignmentY="Center" Stretch="UniformToFill">
<VisualBrush.Visual>
<Label Content="{TemplateBinding TextBox.Tag}" Background="White" Width="45"/>
</VisualBrush.Visual>
</VisualBrush>
</TextBox.Background>
</TextBox>
</ControlTemplate>
</Setter.Value>
</Setter>
</Trigger>
</Style.Triggers>
</Style>

Answer 1

I cannot see whole template but this looks a bit overcomplicated. I assume you're trying to achieve watermark text. For hint use box standard ToolTip property, which by default will display your text in a popup when hover your TextBox but this behaviour can be disabled and ToolTip property reused. You can either create reusable Style - which I prefer - for TextBox, something like this:
<Window ...>
<Window.Resources>
<BooleanToVisibilityConverter x:Key="BooleanToVisibilityConverter"/>
<Style TargetType="{x:Type TextBox}" x:Key="WatermarkTextBoxStyle">
<Setter Property="ToolTipService.IsEnabled" Value="False"/>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type TextBox}">
<Border Background="{DynamicResource {x:Static SystemColors.WindowBrushKey}}"
BorderThickness="1"
BorderBrush="{DynamicResource {x:Static SystemColors.WindowFrameBrushKey}}">
<Grid>
<TextBlock Margin="5,0,0,0"
Text="{TemplateBinding ToolTip}"
Visibility="{Binding RelativeSource={RelativeSource TemplatedParent}, Path=Text.IsEmpty, Converter={StaticResource BooleanToVisibilityConverter}}"
Opacity="0.5"/>
<ScrollViewer Name="PART_ContentHost"/>
</Grid>
</Border>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</Window.Resources>
<TextBox ToolTip="watermark text" Style="{StaticResource WatermarkTextBoxStyle}"/>
</Window>
or, if it's a one-off thing, then do you can do something like this without any Style or Template:
<Grid Background="{DynamicResource {x:Static SystemColors.WindowBrushKey}}">
<TextBlock Margin="5,0,0,0"
Text="watermark text"
Opacity="0.5"
Visibility="{Binding ElementName=myTextBox, Path=Text.IsEmpty, Converter={StaticResource BooleanToVisibilityConverter}}" />
<TextBox Name="myTextBox" Background="Transparent" />
</Grid>