PlaceholderTextResources.xaml

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
					xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
					xmlns:local="clr-namespace:Menees.Windows.Presentation">

	<!--Based on https://prabu-guru.blogspot.com/2010/06/how-to-add-watermark-text-to-textbox.html -->
	<ControlTemplate x:Key="Menees.Windows.Presentation.PlaceholderText.ControlTemplate">
		<ControlTemplate.Resources>
			<Storyboard x:Key="enterGotFocus" >
				<DoubleAnimation Duration="0:0:0.2" To=".2" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="Message"/>
			</Storyboard>
			<Storyboard x:Key="exitGotFocus" >
				<DoubleAnimation Duration="0:0:0.2" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="Message"/>
			</Storyboard>

			<Storyboard x:Key="enterHasText" >
				<DoubleAnimation Duration="0:0:0.1" From=".2" To="0" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="Message"/>
			</Storyboard>
			<Storyboard x:Key="exitHasText" >
				<DoubleAnimation Duration="0:0:0.4" Storyboard.TargetProperty="Opacity" Storyboard.TargetName="Message"/>
			</Storyboard>
		</ControlTemplate.Resources>
		<Border Name="Bd"
							Background="{TemplateBinding Background}"
							BorderBrush="{TemplateBinding BorderBrush}"
							BorderThickness="{TemplateBinding BorderThickness}">
			<Grid>
				<ScrollViewer x:Name="PART_ContentHost" VerticalAlignment="Top" Margin="1" />
				<TextBlock x:Name="Message"
									   Text="{TemplateBinding local:PlaceholderTextHelper.PlaceholderText}"
									   Foreground="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}" IsHitTestVisible="False" Opacity="0.8"
									   HorizontalAlignment="Left" VerticalAlignment="Top" Margin="6,1,0,0"/>
			</Grid>
		</Border>
		<ControlTemplate.Triggers>
			<Trigger Property="IsEnabled" Value="false">
				<Setter TargetName="Bd" Property="Background" Value="{DynamicResource {x:Static SystemColors.ControlBrushKey}}"/>
				<Setter Property="Foreground" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
			</Trigger>
			<Trigger Property="IsEnabled" Value="True">
				<Setter Property="Opacity" Value="1" TargetName="Bd"/>
			</Trigger>
			<MultiTrigger>
				<MultiTrigger.Conditions>
					<Condition Property="local:PlaceholderTextHelper.HasText" Value="False"/>
					<Condition Property="IsFocused" Value="True"/>
				</MultiTrigger.Conditions>
				<MultiTrigger.EnterActions>
					<BeginStoryboard Storyboard="{StaticResource enterGotFocus}"/>
				</MultiTrigger.EnterActions>
				<MultiTrigger.ExitActions>
					<BeginStoryboard Storyboard="{StaticResource exitGotFocus}"/>
				</MultiTrigger.ExitActions>
			</MultiTrigger>

			<Trigger Property="local:PlaceholderTextHelper.HasText" Value="True">
				<Trigger.EnterActions>
					<BeginStoryboard Storyboard="{StaticResource enterHasText}"/>
				</Trigger.EnterActions>
				<Trigger.ExitActions>
					<BeginStoryboard Storyboard="{StaticResource exitHasText}"/>
				</Trigger.ExitActions>
			</Trigger>

		</ControlTemplate.Triggers>
	</ControlTemplate>

	<Style x:Key="Menees.Windows.Presentation.PlaceholderTextBox" TargetType="{x:Type TextBoxBase}">
		<Setter Property="local:PlaceholderTextHelper.IsMonitoring" Value="True"/>
		<Setter Property="local:PlaceholderTextHelper.PlaceholderText" Value="PlaceholderText" />
		<Setter Property="Template" Value="{StaticResource Menees.Windows.Presentation.PlaceholderText.ControlTemplate}"/>
	</Style>

	<Style x:Key="Menees.Windows.Presentation.PlaceholderPasswordBox" TargetType="{x:Type PasswordBox}">
		<Setter Property="local:PlaceholderTextHelper.IsMonitoring" Value="True"/>
		<Setter Property="local:PlaceholderTextHelper.PlaceholderText" Value="Password" />
		<Setter Property="Template" Value="{StaticResource Menees.Windows.Presentation.PlaceholderText.ControlTemplate}"/>
	</Style>
</ResourceDictionary>