title: WPF problem: Need to draw a control on top of another
body: <p>I've a shell window constructed of an Header, Main Content and Footer.
  The main content is a tab control.
  According to the design, one of the tab items content (a user control) needs to expand a little bit over the footer.
  At first I thought about implmenting this with a negative Margin, but the footer no matter what I did always get drawn on top of my content.</p>
  
  <p>For example consider the following xaml:</p>
  
  <pre><code>&lt;Grid&gt;
    &lt;Grid.RowDefinitions&gt;
      &lt;RowDefinition Height="33*"/&gt;
      &lt;RowDefinition Height="33*"/&gt;
      &lt;RowDefinition Height="33*"/&gt;
    &lt;/Grid.RowDefinitions&gt;
    &lt;StackPanel Background="Blue" Grid.Row="0"/&gt; &lt;!-- Header --&gt;
    &lt;StackPanel Background="Red" Grid.Row="2"/&gt;  &lt;!-- Footer --&gt;
    &lt;TabControl Grid.Row="1"  &gt; &lt;!-- Content --&gt;
      &lt;TabItem&gt;
        &lt;Grid&gt;
          &lt;Grid.ColumnDefinitions&gt;
            &lt;ColumnDefinition Width="33*"/&gt;
            &lt;ColumnDefinition Width="33*"/&gt;
            &lt;ColumnDefinition Width="33*"/&gt;
          &lt;/Grid.ColumnDefinitions&gt;
          &lt;StackPanel Grid.Column="1" Background="Yellow" &gt;
            &lt;Button Width="100" Height="50" Content="Text"  /&gt;
          &lt;/StackPanel&gt;
        &lt;/Grid&gt;
    &lt;/TabItem&gt;
  &lt;/TabControl&gt;
  </code></pre>
  
  <p></p>
  
  <p>What I would want to achieve is making the Yellow StackPanel to reach the bottom of the screen somewhow, overlapping on top of the red footer.</p>
  
  <p>Hope it is understandable.
  Thanks
  Ariel</p>