title: How can one link a DataTrigger to whether a ScrollViewer can scroll up?
body: <p>I am wanting to show a half opaque arrow at the top and bottom of my ScrollViewer if it can scroll up or down respectively.  I'm thinking the best option is a DataTrigger, but I'm not sure what I can tie it too.  I'm trying to avoid subclassing ScrollViewer, but if I absolutely have to, I will.  Any ideas?</p>
  
  <p>I'm using the .Net Framework 3.5 (man I wish I could upgrade!).  </p>
  
  <p>Thanks. :)</p>