title: How do I create a WPF Dropdown panel
body: <p>I'd like to create a dropdown panel in WPF the acts like a ComboBox/Expander hybrid. I'm currently using an Expander but it pushes the the controls underneath it down when it expands.</p>
  
  <p>I simply want it to act like a ComboBox and overlay it's dropdown. I've looked at using Popups but they don't move with the underlying window when it's moved.</p>
  
  <p>So, I've concluded that the closest control to my needs is a ComboBox which allows me to put a Grid or StackPanel into its dropdown area.</p>
  
  <p>Any ideas how to achieve this?</p>