MainWindow.xaml

<Window x:Class="WpfApplication147.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Title="MainWindow" Height="350"
        Width="525" xmlns:dxe="http://schemas.devexpress.com/winfx/2008/xaml/editors" xmlns:dxc="http://schemas.devexpress.com/winfx/2008/xaml/core" xmlns:dxet="http://schemas.devexpress.com/winfx/2008/xaml/editors/themekeys"
        xmlns:local="clr-namespace:WpfApplication147">
    <Window.Resources>
        <ResourceDictionary>
            <local:ErrorContentConverter x:Key="ErrorContentToErrorTypeConverter" GetValueTag="ErrorType" Separator=";"/>
            <local:ErrorContentConverter x:Key="ErrorContentConverter" GetValueTag="ErrorContent" Separator=";"/>
            <Style TargetType="{x:Type dxe:ErrorControl}" BasedOn="{StaticResource {x:Type dxe:ErrorControl}}">
                <Style.Triggers>
                    <DataTrigger Binding="{Binding Path=Content.ErrorContent, RelativeSource={RelativeSource Self}, Converter={StaticResource ErrorContentToErrorTypeConverter}}" Value="Critical">
                        <Setter Property="ContentTemplate" Value="{DynamicResource {dxet:ErrorTypesThemeKeyExtension ResourceKey=Critical}}" />
                    </DataTrigger>
                    <DataTrigger Binding="{Binding Path=Content.ErrorContent, RelativeSource={RelativeSource Self}, Converter={StaticResource ErrorContentToErrorTypeConverter}}" Value="Warning">
                        <Setter Property="ContentTemplate" Value="{DynamicResource {dxet:ErrorTypesThemeKeyExtension ResourceKey=Warning}}" />
                    </DataTrigger>
                    <DataTrigger Binding="{Binding Path=Content.ErrorContent, RelativeSource={RelativeSource Self}, Converter={StaticResource ErrorContentToErrorTypeConverter}}" Value="Information">
                        <Setter Property="ContentTemplate" Value="{DynamicResource {dxet:ErrorTypesThemeKeyExtension ResourceKey=Information}}" />
                    </DataTrigger>
                </Style.Triggers>
            </Style>
        </ResourceDictionary>
    </Window.Resources>
    
    <Window.DataContext>
        <local:TestClass TestString="test"/>
    </Window.DataContext>
    
    <StackPanel>
        <dxe:TextEdit EditValue="{Binding Path=TestString, ValidatesOnDataErrors=True, UpdateSourceTrigger=PropertyChanged}">
            <dxe:TextEdit.ErrorToolTipContentTemplate>
                <DataTemplate>
                    <TextBlock Text="{Binding Path=ErrorContent, Converter={StaticResource ErrorContentConverter}}" />
                </DataTemplate>
            </dxe:TextEdit.ErrorToolTipContentTemplate>
        </dxe:TextEdit>
    </StackPanel>
</Window>