Hi, I have written a markup extension which stores amongst others a help text. This help text is shown on the right side of the main window. This works fine. Now, I want to add a tooltip for every control. The content of the tooltip should be same as for the helptext extension. The XAML code: <ListView ctrl:ListViewLayoutManager.Enabled="true" x:Name="ListViewSources" ItemsSource="{Binding SourceItems}" ItemContainerStyle="{DynamicResource ListViewItemStyleAlternate}" Height="150" MinWidth="350" Helper:HelpExtension.IsControl="true" Helper:HelpExtension.HelpText="{x:Static strings:GUIResource.HelpProfilesSourcesDescriptionText}" > <ListView.ToolTip> <ToolTip Style="{DynamicResource Own_TooltipStyle}"></ToolTip> </ListView.ToolTip> And now the code of the style: If I run the program I get the binding error: System.Windows.Data Error: 39 : BindingExpression path error: 'Helper:HelpExtension' property not found on 'object' ''ListView' (Name='ListViewSources')'. BindingExpression:Path=Helper:HelpExtension.HelpText; DataItem='ListView' (Name='ListViewSources'); target element is 'TextBlock' (Name=''); target property is 'Text' (type 'String') Does anybody know how I can bind the TextBlock to the content of Helper:HelpExternsion.HelpText? Thanks Dieter