title: WPF DataGrid Bind Editor Setting to another property
body: <p>I have a field in a DataGrid, bound to a value (Item.Amount), now inside the style for that field editor, i would like to bind the Format field to Item.QuantityDecimalPoints.</p>
  
  <p>But I cannot seem to be able to go up the tree to the same Item that the record is bound to.</p>
  
  <p>I have tried the following:</p>
  
  <pre><code>Format="{Binding Path=QuantityDecimalPoints, RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type DBO:Item}}}"
  </code></pre>
  
  <p>And</p>
  
  <pre><code>Format="{Binding Path=QuantityDecimalPoints, RelativeSource={RelativeSource PreviousData}}"
  </code></pre>