title: ConverterParameter with Binding on Multibinding
body: <p>is it possible to add a Binding to a ConverterParameter in a MultiBinding?
  Something like this:</p>
  
  <pre><code>    &lt;HierarchicalDataTemplate DataType="{x:Type Elements:RootElement}"&gt;
          &lt;HierarchicalDataTemplate.ItemsSource&gt;
              &lt;MultiBinding Converter="{StaticResource filterConverter}" ConverterParameter="{Binding IsFilterd}"&gt;
                  &lt;Binding Path="Children"/&gt;
                  &lt;Binding Path="FilterChildren"/&gt;
              &lt;/MultiBinding&gt;
          &lt;/HierarchicalDataTemplate.ItemsSource&gt;
          &lt;TextBlock Text="{Binding Name}" FontWeight="Normal"/&gt;
      &lt;/HierarchicalDataTemplate&gt;
  </code></pre>
  
  <p>Where IsFiltered is a Property on the Object that the Template is applied on.
  I always get an XAML parser error that the Binding is not correct/allowed in ConverterParameter...
  Or is there some other way to do this??</p>
  
  <p>Greets, </p>
  
  <p>Jürgen</p>