ComplexGroupConverter is a IMultiValueConverter used in MultiBindings in conjuction with the ComplexGroupDataTemplateSelector to enable complex data template hierachies example usage: ... <complex:ComplexGroupConverter x:Key="group-converter"/> <HierarchicalDataTemplate DataType="{x:Type cpn:INet}"> <HierarchicalDataTemplate.ItemsSource> <MultiBinding Converter="{StaticResource group-converter}"> <Binding Path="Definitions"/> <Binding Path="Pages"/> </MultiBinding> </HierarchicalDataTemplate.ItemsSource> <StackPanel Orientation="Horizontal"> <Image Source="net.png" VerticalAlignment="Center"/> <TextBlock Text="{Binding Path=Label}"/> </StackPanel> </HierarchicalDataTemplate>