title: DataContext accessible from IMultiValueConverter
body: <p>I have WPF application and I need to bind two arguments (no matter what they are) to calculate the value (checkbox checked or not). So I have to use <code>IMultiValueConverter</code> and that's fine.</p>
  
  <p>But is there a way, to give this converter access to <code>DataContext</code> (ViewModel) of a window I am binding to? </p>
  
  <p>Basically I have some checkboxes in treeview, i need to pass to converter content (text) of theese checkboxes and its parent's header. Then in converter I need to process that text and find out if it's present  in some collection I have in my ViewModel (<code>DataContext</code>). I know that I cannot use ConverterParameter, because it doesn't support binding.</p>