Planco de espaço reservado WPF
<TextBox
x:Name="tbxSeach"
Grid.Row="0"
Grid.Column="0"
Height="25"
Margin="10,0,10,0"
HorizontalAlignment="Stretch"
VerticalAlignment="Bottom"
VerticalContentAlignment="Center"
Text="{Binding SearchText, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}"
TextAlignment="Left">
<TextBox.Resources>
<VisualBrush
x:Key="hinttext"
AlignmentX="Left"
Stretch="None"
TileMode="None">
<VisualBrush.Visual>
<TextBlock
FontStyle="Italic"
Foreground="#959595"
Text="Search..." />
</VisualBrush.Visual>
</VisualBrush>
</TextBox.Resources>
<TextBox.Style>
<Style BasedOn="{StaticResource TextBoxBase}" TargetType="TextBox">
<Setter Property="VerticalAlignment" Value="Center" />
<Setter Property="FontSize" Value="12" />
<Setter Property="Background" Value="Transparent" />
<Style.Triggers>
<Trigger Property="Text" Value="">
<Setter Property="Background" Value="{StaticResource hinttext}" />
</Trigger>
<Trigger Property="Text" Value="{x:Null}">
<Setter Property="Background" Value="{StaticResource hinttext}" />
</Trigger>
</Style.Triggers>
</Style>
</TextBox.Style>
</TextBox>
Sore Stork